I wanted to edit a custom name of a stylistic set, but since a couple of versions, glyphs won’t let me type in the custom field of the features (see screenshot #1). I am on Glyphs 1349 / macOS 10.14.6, but it was the same on 1348.
Funnily enough, on my MacOs 10.13.6 (High Sierra) I can write in that custom field, but I am restricted to really short line length (see screenshot #2)
Thanks in advance!
Diana
addition: I CAN write in that field if I make the Font Info window wide enough. At a certain width, I can only write a few characters per line, narrower and I can’t write anything. If I make the Font Info box very wide, I can write without a problem. Still a bug though, but not dependent on OS, though 
Interesting, thanks for reporting!
Interestingly enough i’ve just run into that same error on Glyphs Version 2.6.6 (1348) running on macOS Catalina 10.15.7 (19H15).
I can also write if i change the window size but what a weird bug that is.
Resizing the window triggers a re-layout of the views and that fixes the misalignment of the text view.