I have this odd issue in one file that I cannot access or ‘enter’ the background. Whether I press the shortcut or use the command via the menu, I can’t get into the background layer. I can see it and hide it, I can paste outlines to it via CMD+J, but I can’t get there.
Try the latest beta please. Go to Glyphs > Preferences > Updates, activate both checkboxes and press the Update button.
I vaguely remember this issue. Would appear under certain circumstances, I think it is fixed in the 3.3 betas. What are your settings in Font Info > Other?
This is very odd. It seems to be related to the OT features. When I activate the calt for the preview, I can no longer access the background, when I deactivate it, it works again.