Not sure if this is a local issue with my Mac somehow, but I have to press Shift+Space to get the preview that was available with Space before, and then it gets stuck on the Pan mode with the hand, which I have change tools (i.e. press ‘v’) to get out of
Maybe same issue as I have. I have however figured it out why it happens. Could be related to your problem.
Here it goes:
If I connect an external keyboard without first having used the space bar in Glyphs to preview or zoom with Space+CMD I have to press SHIFT to make anything happen.
If I just use the space bar one time and then connect my external USB-keyboard all works fine until the next time I restart the computer.
Strange.
Hey Göran, thanks I do actually have an external keyboard and thought it may be related but, I unplugged the keyboard and am still using my laptop one, same problems.
Edit: I restarted my computer, then space-previewed without the external keyboard plugged in and then plugged the keyboard in and it works now! Odd…
I had a same problem, but the reason was my Intuos. When I plugged in mouse and click a few times, preview by pressing space bar started to work.
Now, when it doesn’t (from time to time) I have to click mouse. Rocket science.
Hmm, interesting, I also have a Wacom tablet. Well I’ll just plug and unplug if it comes up again.
I also have Wacom pen 
There seems to be some system shortcut eating the keyboard events. I can not replicate this. I can use my keyboard in any combination … I have no wacom to test any interference with it.