When I installed Parallels Tools after the update to Parallels 15 my Ubuntu installations were messed up. Specifically for the standard Ubuntu 18.04 the autologin didn't work any more and for Xubuntu, which I have configured to start in text mode, startx just hangs instead of starting X. In both cases I installed Parallels tools via the yellow exclam button in X.
I'm not sure if it's the same issue, but installing Parallels 15 Tools messes my Ubuntu as well. On the startup I get only this message and it hangs (see screenshot). I tried to reset to last snapshot, could start again, but after installing Parallels 15 Tools it does not start again, giving the same message...
When I tried to retry the procedure in order to get a report and it worked this time... I've run the installation of Parallels Tools, when Ubuntu was in the window and not full screen, I am not sure that was it, but it worked. It was the only thing which was differed from the last tries. For me it is fine now
Apparently this has to do with the video driver in the new tools. I read somewhere that gdm3 autologin stands and falls with the video driver. This also explains the problems I have with the new tools and Xubuntu. I changed the autologin to a delayedautologin with 1 second delay and it works now. Now on to my Xubuntu VM...