Haeccine (which is used in the vulgate in a couple places, including Dt 32: 6) and Hiccine (In 1 Reg 21: 15) are not recognized by accenteur, and show as red. Hæccine, when the ligature is used does not show as red, but does not get an accent marked.

adiuva etc. not recognized.

Jakub Jelinek: "Another thing I ran into is that at least the demo accenteur web interface requires one to strip all the accents from the text first (which can be done easily e.g. with sed, sure), maybe it would be useful to work also on previously accented words, do nothing if the accent is correct, use some way to mark errors when there is accent that shouldn't be there or is on an incorrect syllable. That way one could easily use accenteur to just verify if the accents are correct."

Accenteur gives Iésu and Mariǽ…

In the Liber Usualis, Israélis is given in the second verse of Psalm 146, so I would expect that that is the correct form rather than Isráelis, but I am honestly not sure about this.

Benedic does not give an accent, and when input as bénedic it removes the accent

Iusti (uppercase)
sanguinem (-is etc.)

Pharisaei produces

pharisǽi?pharísæi

but since the æ counts as a long vowel, there should be no pharísæi option.

This happens for almost every case of this noun.

cordium generates no accent and removes an accent if one is given. It should instead give córdium

coegerunt doesn't work.