Thanks, Mac.

The Triplet Resolution (Swing) box is ticked, and there are three vertical dotted lines in Editable Notation for each crotchet (1/8 note).

These triplets are being played correctly by BIAB, and are rendered correctly in a rendered file (WAV or MP3), it's just that the Notation Window and the Leadsheet show them incorrectly. The same phrase appears three times in the piece, and the situation is the same each time.

I'll have a look at the start and duration details, and see if tweaking them makes the notation more stable.