Possibly related:-
In another thread, there was an issue with partitions being apparently mis-aligned during the partitioning stage of installation (by KDE Partition Manager).
A question for anyone with deeper insight: Could this overall slowness be an artifact of a similar occurrance?
OK. Nevermind that.
I found stack smashing detected #1198, which indicates a bug in udisks, and udisksd keeps crashing when starting sddm and kde which is possibly more relevant to this thread.
libblockdev v3.0.4 seems to have addressed these issues, two weeks ago.
I suppose it’s a matter of waiting for the fix to filter down to the lower levels.
Cheers.