When I use RMX Scaler in Glyphs 2.4.2 (986) the contents of the selected glyph disappear. I’m doing this in the font tab with a two-master file, testing on a single glyph. RMX Scaler with Glyphs 2.4.1 (983) works.
It works for me. What version of the scaler do you have?
Could you send me the .glyphs file (maybe only the glyph that has the problem)? Then I can have a look as well.
I had the same yesterday in 2.4.3 (1064), but then I ‘undo’ and ‘redo’ it worked fine.