Thanks, Ray. I'm not sure there's a particular xxxx_config.xml file involved and it does not *look* to be related to an INDI driver. Seems to be Kstars itself crashing.
I have noticed a few times on my Ubuntu Mate install that it reports the Marco window manager has crashed, and I have a couple of odd-seeming issues that could be related to the window manager (a fair number of windows within Ekos and within PHD2 appear without any 'minimize' or 'close' widgets).
I am installing the nightly, to see if that will write a new version of some KStars file that might have gotten corrupted. If worst comes to worst I might need to back all the way up and install an earlier version of Ubuntu.