[BetterRed]

@Rob557 - did you try Library Maintenance->Restore database. It could be some library specific preferences (eg VL definitions) went awry, sometimes a database rebuild will fix. I would resolve any Check Library issues and backup my library before doing it.

On occasions I've had to edit the metadata_db_prefs_backup.json file to get rid of the 'malformed' data - I cant recall if it was VL or View Manager preferences. Take a copy of the file before you edit it - you can look at it when you're redoing the VL etc preferences/configuration.

AFAIK - tilde doesn't cause any problems within an EPUB, I use them frequently to indicate 'approximately' - eg "there are ~23M people in Australia".

And AFAIK the tilde has no significance in file names in the sense that <>:"/\|?* are disallowed in Windows. I use !#^~ at the start of folder names (not calibre library folder names) to force sorting into groups - bang, crunch, hat and squiggle indicate 'status' for my image, audio, video collections. I've used them for decades in DOS, Windows, Linux/Ext4 and Solaris/NFS - and probably OS2/HPFS, and various DEC OS's.

BR