That means it is a plug-in that is crashing Glyphs.
I just uploaded version 1204. That should finally fix this for good.
It works! thanks! 
Thank you, Georg!
It works fine with my Mojave machine in the office.
Let’s cross fingers that it will also do on the old Macbook at home. I will keep you informed.
On my old El Capitan book Glyphs tells me »Glyphs 2.6 is currently the newest version available.«
Is that because of my OS version or have you deleted the most recent betas again?
We are speaking about the cutting edge version. You need to activate it in Preferences > Updates. But as you see, it crashes sometimes.