Quoted from a different thread...

Quote Originally Posted by mherger View Post
>> One potential issue with the
>> logitechmediaserver-7.9.0-0.10.20140508git1399582156 update, I've just
>> noticed. Re-scan "new and changed" seems to be locking the web-gui out
>> of the database. Can't remember, but I don't think this was the previous
>> behaviour. Might have something to do with Michael's recent db
>> "optimisations".
>
> I definitely don't see this behavior on Windows. FWIW.

It could be the VACUUM step at the end of a scan. Depending on your
library size and I/O performance this can take a while, during which the
web UI is non-responsive. It should only be run if no player is active.
You might not have seen it if the step was skipped due to some player
playing music in the background.
Maybe rethink the idea of having a daily scheduled vacuum instead? How about replacing the 'Rescan Music Library' plugin with one that can both rescan the library and vacuum the dbs? Call it 'Server & Database Maintenance' or something similar. Other things could be added to the plugin as desired, such as clearing the server.log (I do this on a daily basis as well).