Master compatibility suddenly won't show

I was working on a glyphs file with two masters, had to close it, then opened it back up again. Now, all of my red triangles on the bold master (the one I’m working to complete) are gone. Before I closed the app, every blank character had a red triangle above it.

Also when editing a glyph, I am unable to see the yellow or red colors on incompatible paths, and I’m unable to see the dark blue lines that show where the anchor point is on the other master. What is going on and how can I fix it?

I have Glyphs Version 2.6.1 (1230).

For new files, empty glyphs sometimes wrongly show the red mark.
And you need at least one instance that interpolates to trigger the incompatibility warnings.