Original report by Matti Immonen on Facebook is failure to load Hybris (SPS IPF 1457) on a stock A500 with TEAC FD-235F-161-U after writing the IPF to disk using GW v0.15 and a Sony MPF920 drive. Many other IPFs (including the slightly tricky Xenon 2, SPS IPF 2234) loaded fine on the same test system. Additionally, an earlier conversion of the IPF to HFE (using HxC tools) loaded fine on the same test system using FlashFloppy/Gotek.
The cause is apparently the use of custom sync words with MFM-invalid sequences of zeroes. Matti wrote the IPF to several disks, some of which worked somewhat better than others (but none actually load 100%). He then dumped those disks to SCP using Greaseweazle on the offending Amiga TEAC drive (images: https://drive.google.com/open?id=1JDF0_ZVL4W9BbjqyK2F1Z6dhITRtIUef).
The offending SCP images do not load properly in emulation, and analysis with Disk-Utilities indicates bad tracks. The following tracks in file Teac_Hybris_bad_disk.scp are unloadable: 3.1 (5412), 4.1 (5241), 6.0 (a429), 14.1 (5412), 15.0 (5241), 16.0 (a429), 17.0 (2541), 19.1 (2541), 30.0 (2541), 44.1 (a425), 50.0 (5412), 62.1 (2541).
The bad syncs are: 5412 (3), 5241 (2), 2541 (4), a429 (2), a425 (1).
Take Track 3.1 with sync 5412 = 0101 0100 0001 0010, which has an MFM-illegal sequence of five zeroes. This is a flux interval of 12us. Cowlark Fluxengine author reports problems at around 10us (ref http://cowlark.com/fluxengine/doc/technical.html). Searching for the sync word manually in Disk-Utilities we find 5592 = 0101 0101 1001 0010: Two bits in the five-zero sequence have been flipped! Note that syncs 5241 and 2541 are similarly afflicted with a five-zero sequence in their 41 byte.
Take Track 6.0 with sync a429 = 1010 0100 0010 1001, which has an illegal sequence of four zeroes (flux interval 10us). Searching manually in Disk-Utilities we find sync a5a9 = 1010 0101 1010 1001: Again two-adjacent bits in the four-zero sequence have been flipped! Further, we can print the exact flux intervals in the bad sync word (ns): 3950, 6000, 3525, 2375, 3825, 3825, 6000. Note the expected interval 10000 has been split into 3525+2375+3825 by the drive.