Unfortunately the question "has it ever worked?" has not been answered yet.
Can you work on the NAS command line? I'd start by deleting the
library.db. Check where the cache folder is located in
Settings/Information. Then restart LMS. If the file itself was corrupted
this would sort it out.
Then make sure your file system has enough free disk space. Once you've
figured out the cache folder's location run "df -h" and compare whether
the cache folder is on a partition with plenty of disk space.
Check the cache folder: are there huge files you might want to remove,
eg. all the *.db files? You can safely delete them, they would be
rebuilt upon next start.
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