tonight I experienced also this problem. It was my first session with KStars 3.5.6 (PPA) after upgrading from 3.5.5. I have KStars + INDI on a Ubuntu Mate 20.04 x86_64 box, and use a AZ-EQ6 (eqmod) mount.
In my case, I run the PA assistant using the guide camera/scope for faster refresh (my imaging camera is a slow CCD), but this seems to have no effect over this issue. The PA assistant captures and solves the first image, then does the first slew. After this slew the UI went somewhat crazy, "Capture&Solve" grayed out and reenabled in a loop. In the Mount tab in Ekos the coordinates were "jumping" although the mount wasn't slewing. Then I noticed that it was reporting Meridian flip, pending, running. First thing I did after cancelling the PA was purge the configuration of eqmod and set it to the defaults (it also was updated along with KStars and some other INDI modules; in the past I once ran into problems with configuration files of updated drivers). Not to avail. Then, I disabled "Flip if HA>" (which I always had set to 2 deg) and re-run PAA and everything went as normal (as I read now that the other posters did as well).
Before KStars 3.5.6, this never happened to me. I will try to retrieve logs later to see if they help.