WetGeek I have an issue with my Plasma laptop.
At the risk of making this another long message, I won't detail everything I've tried for the last hour, but just report my current status. Trying an X11 session was no help. Changing to the Unstable repo didn't help, either. An update afterwards upgraded 200 packages, but all I've noticed so far is that it changed my background to a silly graphic and I wasn't able to start Latte. I attributed that to a work in progress. But after changing the repo back to Shannon, those changes remained. Just something more to wonder about.
Interestingly enough, I have no problems updating my wife's Latitude, which is the identical model to my two, and also running Plasma. That's encouraging, although I still don't like this sort of mystery. And likewise with my little ACER Travelmate laptop, which also uses Plasma. Update was normal, and no issues with it at all.
At the very beginning of all this earlier this morning, I did an update on this Plasma laptop that only installed 18 upgraded packages. I wrote that off as to be expected, since Plasma 6 is still to come. But all of the other updates I've done since then have installed 180-200 upgraded packages. It was just possible - but not likely - that I'd not updated those machines the last time, which might explain why their updates were so big this time. But I'm pretty sure that didn't happen. So, the 18 package update on my main laptop this morning must be a clue of some kind.
I can probably reinstall the OS on this machine and cure whatever problem is has, but then I'll need to recreate the 200 or so email filters I just got done creating after the last installation, and reconfiguring Thunderbird and Vivaldi are not trivial tasks. So I'm going to try everything else I can think of before I do that. Like I said earlier, no worries - I have plenty of other options to access my NAS in the meantime.