I've encountered this strange problem in MC18, where all my files are suddenly missing their path and of course they cannot be played back when this happens. It has happened a few times since upgrading to 18. The only solution has been to delete all files from the library and import everything again manually or let auto-import do it.
I do think every time I've seen this behavior the program has just crashed previous to it happening. I might come home from work and turn on my tv and see that MC has crashed (I always leave my machine on and MC running to let it auto-import all the time) and when I restart MC the files are all missing the path. I have no idea how I would reproduce this behavior either since I'm never there when it happens. I could leave logging on, but the log would probably grow huge from the time I turn it on until the problem happens again.
I've attached a picture of my auto-import config. As you can see all the files are sourced from network drives, but this server is always on and the problem did not exist in MC17 so I can't see that being the problem.
This is of course a huge pain when I've got over 300 000 files (don't ask
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