Ornament glyphs seem to corrupt over time in Illustrator

I made a showing of my borders & ornaments in Illustrator in 2020 for my site (top), after which I continued to revise the font files. Over time, the original .ai artwork has started to degrade for some reason, so that it now looks as it does in the bitmap on the bottom.

I did not use the ornm feature: I simply gave each glyph a descriptive name (e.g. ornTile02B or fleuronF).

Does this make sense to anyone? Did I build the font wrong?

Possible clue: when I tried to save a png of the ‘corrupted’ art just now, I got a prompt warning me that “Some names of the files being saved contain non-Latin characters.” The full name of the file in question is ‘CorruptedOrns.jpg’

It could be the same issue: Manually inserted glyphs in Adobe Illustrator are changed when glyphs are added/deleted in the Glyphs App

Thanks, Georg. Sounds plausible.