No need to apologize, Brent. You are a help. I believe I have narrowed pretty close to the problem.
The issue is not with copying - this can happen when simply viewing photos in the browser itself.
I believe the issue is with some cache or settings or another - I deleted
~/.config/nautilus/* and it worked perfectly - for about 20 minutes of photo viewing with occasional (successful) copies. I expect it built back up a cache, possibly of thumbnails (though I think those should be in
~/.cache/thumbnails), which led to its crash.
Currently she is tasked with testing whether or not Caja leads to the same behavior. In the mean time, if any of you can offer suggestions for Nautilus (are there back-end settings that can disable certain types of caching?), I would appreciate that deeply.
Brent - I will check out journalctl ASAP. Work is eating about 12hr/day, so I probably won't take the time for a few days, but I will try.