I tried to get an SVG version of a sample seqdiag diagram via Kroki CLI and found out that
the SVG code is doubled — repeated two times instead of one.
I've attached an SVG. As you can see, all the code from
<rect fill="rgb(0,0,0)" height="111" style="filter:url(#filter_blur);opacity:0.7;fill-opacity:1" width="8" x="127" y="141" />
<text fill="rgb(0,0,0)" font-family="sans-serif" font-size="11" font-style="normal" font-weight="normal" text-anchor="middle" textLength="19" x="341.5" y="198">2st</text>
is repeated twice.
<svg xmlns="http://www.w3.org/2000/svg" xmlns:inkspace="http://www.inkscape.org/namespaces/inkscape" xmlns:xlink="http://www.w3.org/1999/xlink" style="width: 640px; height: 274px;">
<defs id="defs_block">
<filter height="1.504" id="filter_blur" inkspace:collect="always" width="1.1575" x="-0.07875" y="-0.252">
<feGaussianBlur id="feGaussianBlur3780" inkspace:collect="always" stdDeviation="4.2"></feGaussianBlur>
</filter>
</defs>
<title>blockdiag</title>
<desc></desc>
<rect fill="rgb(0,0,0)" height="111" style="filter:url(#filter_blur);opacity:0.7;fill-opacity:1" width="8" x="127" y="141"></rect>
<rect fill="rgb(0,0,0)" height="111" style="filter:url(#filter_blur);opacity:0.7;fill-opacity:1" width="8" x="319" y="141"></rect>
<rect fill="rgb(0,0,0)" height="46" style="filter:url(#filter_blur);opacity:0.7;fill-opacity:1" width="8" x="511" y="206"></rect>
<rect fill="rgb(0,0,0)" height="40" stroke="rgb(0,0,0)" style="filter:url(#filter_blur);opacity:0.7;fill-opacity:1" width="128" x="67" y="46"></rect>
<rect fill="rgb(0,0,0)" height="40" stroke="rgb(0,0,0)" style="filter:url(#filter_blur);opacity:0.7;fill-opacity:1" width="128" x="259" y="46"></rect>
<rect fill="rgb(0,0,0)" height="40" stroke="rgb(0,0,0)" style="filter:url(#filter_blur);opacity:0.7;fill-opacity:1" width="128" x="451" y="46"></rect>
<path d="M 128 80 L 128 262" fill="none" stroke="rgb(0,0,0)" stroke-dasharray="8 4"></path>
<rect fill="moccasin" height="111" stroke="rgb(0,0,0)" width="8" x="124" y="135"></rect>
<path d="M 320 80 L 320 262" fill="none" stroke="rgb(0,0,0)" stroke-dasharray="8 4"></path>
<rect fill="moccasin" height="111" stroke="rgb(0,0,0)" width="8" x="316" y="135"></rect>
<path d="M 512 80 L 512 262" fill="none" stroke="rgb(0,0,0)" stroke-dasharray="8 4"></path>
<rect fill="moccasin" height="46" stroke="rgb(0,0,0)" width="8" x="508" y="200"></rect>
<rect fill="rgb(255,255,255)" height="40" stroke="rgb(0,0,0)" width="128" x="64" y="40"></rect>
<text fill="rgb(0,0,0)" font-family="sans-serif" font-size="11" font-style="normal" font-weight="normal" text-anchor="middle" textLength="19" x="128" y="66">End</text>
<rect fill="rgb(255,255,255)" height="40" stroke="rgb(0,0,0)" width="128" x="256" y="40"></rect>
<text fill="rgb(0,0,0)" font-family="sans-serif" font-size="11" font-style="normal" font-weight="normal" text-anchor="middle" textLength="37" x="320" y="66">stage1</text>
<rect fill="rgb(255,255,255)" height="40" stroke="rgb(0,0,0)" width="128" x="448" y="40"></rect>
<text fill="rgb(0,0,0)" font-family="sans-serif" font-size="11" font-style="normal" font-weight="normal" text-anchor="middle" textLength="37" x="512" y="66">stage2</text>
<path d="M 136 135 L 312 135" fill="none" stroke="rgb(0,0,0)"></path>
<polygon fill="rgb(0,0,0)" points="304,131 312,135 304,139" stroke="rgb(0,0,0)"></polygon>
<path d="M 328 200 L 504 200" fill="none" stroke="rgb(0,0,0)"></path>
<polygon fill="rgb(0,0,0)" points="496,196 504,200 496,204" stroke="rgb(0,0,0)"></polygon>
<text fill="rgb(0,0,0)" font-family="sans-serif" font-size="11" font-style="normal" font-weight="normal" text-anchor="middle" textLength="19" x="149" y="133">1st</text>
<text fill="rgb(0,0,0)" font-family="sans-serif" font-size="11" font-style="normal" font-weight="normal" text-anchor="middle" textLength="19" x="341" y="198">2st</text>
</svg>
<svg xmlns="http://www.w3.org/2000/svg" xmlns:inkspace="http://www.inkscape.org/namespaces/inkscape" xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 0 640 274" width="640px" height="274px">
<defs id="defs_block">
<filter height="1.504" id="filter_blur" inkspace:collect="always" width="1.1575" x="-0.07875" y="-0.252">
<feGaussianBlur id="feGaussianBlur3780" inkspace:collect="always" stdDeviation="4.2"/>
</filter>
</defs>
<title>blockdiag</title>
<desc>seqdiag {
start [label = "Contract"]
start [label = "End"]
start -> stage1 [label = "1st"];
stage1 -> stage2 [label = "2st"];
}</desc>
<rect fill="rgb(0,0,0)" height="111" style="filter:url(#filter_blur);opacity:0.7;fill-opacity:1" width="8" x="127" y="141"/>
<rect fill="rgb(0,0,0)" height="111" style="filter:url(#filter_blur);opacity:0.7;fill-opacity:1" width="8" x="319" y="141"/>
<rect fill="rgb(0,0,0)" height="46" style="filter:url(#filter_blur);opacity:0.7;fill-opacity:1" width="8" x="511" y="206"/>
<rect fill="rgb(0,0,0)" height="40" stroke="rgb(0,0,0)" style="filter:url(#filter_blur);opacity:0.7;fill-opacity:1" width="128" x="67" y="46"/>
<rect fill="rgb(0,0,0)" height="40" stroke="rgb(0,0,0)" style="filter:url(#filter_blur);opacity:0.7;fill-opacity:1" width="128" x="259" y="46"/>
<rect fill="rgb(0,0,0)" height="40" stroke="rgb(0,0,0)" style="filter:url(#filter_blur);opacity:0.7;fill-opacity:1" width="128" x="451" y="46"/>
<path d="M 128 80 L 128 262" fill="none" stroke="rgb(0,0,0)" stroke-dasharray="8 4"/>
<rect fill="moccasin" height="111" stroke="rgb(0,0,0)" width="8" x="124" y="135"/>
<path d="M 320 80 L 320 262" fill="none" stroke="rgb(0,0,0)" stroke-dasharray="8 4"/>
<rect fill="moccasin" height="111" stroke="rgb(0,0,0)" width="8" x="316" y="135"/>
<path d="M 512 80 L 512 262" fill="none" stroke="rgb(0,0,0)" stroke-dasharray="8 4"/>
<rect fill="moccasin" height="46" stroke="rgb(0,0,0)" width="8" x="508" y="200"/>
<rect fill="rgb(255,255,255)" height="40" stroke="rgb(0,0,0)" width="128" x="64" y="40"/>
<text fill="rgb(0,0,0)" font-family="sans-serif" font-size="11" font-style="normal" font-weight="normal" text-anchor="middle" textLength="19" x="128.5" y="66">End</text>
<rect fill="rgb(255,255,255)" height="40" stroke="rgb(0,0,0)" width="128" x="256" y="40"/>
<text fill="rgb(0,0,0)" font-family="sans-serif" font-size="11" font-style="normal" font-weight="normal" text-anchor="middle" textLength="37" x="320.5" y="66">stage1</text>
<rect fill="rgb(255,255,255)" height="40" stroke="rgb(0,0,0)" width="128" x="448" y="40"/>
<text fill="rgb(0,0,0)" font-family="sans-serif" font-size="11" font-style="normal" font-weight="normal" text-anchor="middle" textLength="37" x="512.5" y="66">stage2</text>
<path d="M 136 135 L 312 135" fill="none" stroke="rgb(0,0,0)"/>
<polygon fill="rgb(0,0,0)" points="304,131 312,135 304,139" stroke="rgb(0,0,0)"/>
<path d="M 328 200 L 504 200" fill="none" stroke="rgb(0,0,0)"/>
<polygon fill="rgb(0,0,0)" points="496,196 504,200 496,204" stroke="rgb(0,0,0)"/>
<text fill="rgb(0,0,0)" font-family="sans-serif" font-size="11" font-style="normal" font-weight="normal" text-anchor="middle" textLength="19" x="149.5" y="133">1st</text>
<text fill="rgb(0,0,0)" font-family="sans-serif" font-size="11" font-style="normal" font-weight="normal" text-anchor="middle" textLength="19" x="341.5" y="198">2st</text>
<rect fill="rgb(0,0,0)" height="111" style="filter:url(#filter_blur);opacity:0.7;fill-opacity:1" width="8" x="127" y="141"/>
<rect fill="rgb(0,0,0)" height="111" style="filter:url(#filter_blur);opacity:0.7;fill-opacity:1" width="8" x="319" y="141"/>
<rect fill="rgb(0,0,0)" height="46" style="filter:url(#filter_blur);opacity:0.7;fill-opacity:1" width="8" x="511" y="206"/>
<rect fill="rgb(0,0,0)" height="40" stroke="rgb(0,0,0)" style="filter:url(#filter_blur);opacity:0.7;fill-opacity:1" width="128" x="67" y="46"/>
<rect fill="rgb(0,0,0)" height="40" stroke="rgb(0,0,0)" style="filter:url(#filter_blur);opacity:0.7;fill-opacity:1" width="128" x="259" y="46"/>
<rect fill="rgb(0,0,0)" height="40" stroke="rgb(0,0,0)" style="filter:url(#filter_blur);opacity:0.7;fill-opacity:1" width="128" x="451" y="46"/>
<path d="M 128 80 L 128 262" fill="none" stroke="rgb(0,0,0)" stroke-dasharray="8 4"/>
<rect fill="moccasin" height="111" stroke="rgb(0,0,0)" width="8" x="124" y="135"/>
<path d="M 320 80 L 320 262" fill="none" stroke="rgb(0,0,0)" stroke-dasharray="8 4"/>
<rect fill="moccasin" height="111" stroke="rgb(0,0,0)" width="8" x="316" y="135"/>
<path d="M 512 80 L 512 262" fill="none" stroke="rgb(0,0,0)" stroke-dasharray="8 4"/>
<rect fill="moccasin" height="46" stroke="rgb(0,0,0)" width="8" x="508" y="200"/>
<rect fill="rgb(255,255,255)" height="40" stroke="rgb(0,0,0)" width="128" x="64" y="40"/>
<text fill="rgb(0,0,0)" font-family="sans-serif" font-size="11" font-style="normal" font-weight="normal" text-anchor="middle" textLength="19" x="128.5" y="66">End</text>
<rect fill="rgb(255,255,255)" height="40" stroke="rgb(0,0,0)" width="128" x="256" y="40"/>
<text fill="rgb(0,0,0)" font-family="sans-serif" font-size="11" font-style="normal" font-weight="normal" text-anchor="middle" textLength="37" x="320.5" y="66">stage1</text>
<rect fill="rgb(255,255,255)" height="40" stroke="rgb(0,0,0)" width="128" x="448" y="40"/>
<text fill="rgb(0,0,0)" font-family="sans-serif" font-size="11" font-style="normal" font-weight="normal" text-anchor="middle" textLength="37" x="512.5" y="66">stage2</text>
<path d="M 136 135 L 312 135" fill="none" stroke="rgb(0,0,0)"/>
<polygon fill="rgb(0,0,0)" points="304,131 312,135 304,139" stroke="rgb(0,0,0)"/>
<path d="M 328 200 L 504 200" fill="none" stroke="rgb(0,0,0)"/>
<polygon fill="rgb(0,0,0)" points="496,196 504,200 496,204" stroke="rgb(0,0,0)"/>
<text fill="rgb(0,0,0)" font-family="sans-serif" font-size="11" font-style="normal" font-weight="normal" text-anchor="middle" textLength="19" x="149.5" y="133">1st</text>
<text fill="rgb(0,0,0)" font-family="sans-serif" font-size="11" font-style="normal" font-weight="normal" text-anchor="middle" textLength="19" x="341.5" y="198">2st</text>
</svg>