Hi,
I installed the latest nightly build using PPA and noticed that Kstars crashes while doing ASTAP plate solving.
I did not try astrometry solver, it may have the same issue too.
The problem went away once I switched back to the stable version.
My system is RPi4, Ubuntu 18.04.
I too have Ubuntu 18.04. Both version 3.9 and 4.0 crash every time I use the assignment plate solving routine now. It crashes right before the FINAL iteration is completed, but AFTER the scope has moved. So I now have to wait for the crash, relaunch Kstars/Ekos, and continue. I've found that I can solve and sync with no problem, but solving and slewing crashes my system every time.
I had the same issue last night, crashing in the plate solver (in my case it was with local astrometry.net), but I looked into it and it was actually crashing while creating the image display. I did make a fix for that that was submitted last night. Can you let me know if you still see a crash?