From what I saw Cosmic has a lot of potential and looks pretty sleek too, right now I'm using KDE it's a great desktop, but now that I have a second monitor it randomly crashes on me, I think I'll switch to Cosmic when it reaches beta.
I'm guessing that's the onboard AMD graphics then?
If you do an lspci -k | grep -EA3 'VGA|3D|Display' what does it return? Are you able to find anything in dmsg (journalctl -xb-1 for previous boot log) that would give an error message to investigate?