Optical margin
Optical margin behaves oddly in InDesign 19.0. I've attached a screen recording showing this behavior:
This is a file that had been created in a previous version of ID—probably 13 or so—and has handled migration to subsequent versions gracefully. However, when I opened it in 19 and attempted to edit some text, the optical margin in that paragraph behaves strangely, turning itself off on certain lines.
Deactivating and reactivating optical margin does not correct it. Some adjustment is made, but not enough.
I haven't been able to reproduce this behavior in text blocks created in 19, so it appears to be an issue with files created in previous versions of ID.