I'm not actually using MTP to transfer files. I've been pushing
them to the device with adb instead. The files were on the
device, but you're right, I mixed up MTP server and mediascanner.
It looks like both crashed, but mediascanner's crash file is
dated after I noticed the issues. It's possible that it could
have crashed more than once and I only see the latest dump.
Yes, it all worked on second boot.
The number and frequency of crashes has me a bit concerned. I
ended up with ten crash files in under an hour of use.