Some further information. This is still continuing, and growing the library. I now have many duplicate entries for every song in my library. I have uninstalled MC26, and re-installed, then rebuilt the library - but to no avail.
The problem seems to stem from the ImportNew Files and the AnalyzeDrive: Drive does not exist entries in the log. Am I reading too much into the log entries to be suspicious of the swapping of the directory delimiters from '\\' to '//'?
This is running on Windows 10, so the '//' entries are correct, but not the '\\'.
I don't know if it is relevant, but I also have MC26 running as a Server on Linux, and I sometimes connect this Windows instance as a client to that server - that seems to work okay, but maybe is has screwed up a registry entry somehow.
When I uninstalled MC26, I was asked if I should remove MC library files, which I should not do if upgrading, so I didn't.
That will be my next step. I will be interested if anyone else has problems connecting MC between Windows and Linux.
Duncan