About once a day the zoom keyboard shorcuts (cmd+ and cmd-) stop working and I have to restart Glyphs. This seems to be one of those bugs related to opening/closing/changing tabs and various functions being unresponsive. Sometimes corruption of the preview area coincides. I have seen this in 1.3.20, and I think it also happened in the final build of 1.3.19.
Anything in the console when this happens?
Nothing.
I will have a look at it. It never happened to me, so it may take a while until I can fix this.