CalDAV/CardDAV client data overwrites server new account

I have oC on a hosted VM using Sqlite, mainly using Contact and Calendar apps with iOS CalDAV/CardDAV clients on 2-way sync. The setup has been working well for years. A few days ago I noticed that clients are not getting one another's new calendar entries, so decided to check on oC's web UI, but got an "Internal Server Error" screen instead of the login prompt.

Having backed up the oC tree, I manually fresh installed oC 8.0.16 and all worked. As soon as I replaced the config and data directories, or just the db file, I got the "Internal Server Error" again. The old db file content seems very readable using DB Browser. I also made sure the old non-working db permissions match those of the working new blank db.

The host recently relocated their datacentre. Tech support isn't telling me whether they changed anything, but said many customes reported Sqlite3 problems and suggested me to connect to MySQL instead. I know this is also recommended by oC but I just want to get it going first.

Since I can't be sure whether the db file is sound, but I do know that it's 3 weeks outdated while the iOS clients have the latest full dataset, would it be possible to sync the existing iOS devices and its client accounts with a fresh oC 8.0.16 server newly set up with the same user credentials but with blank db file? Will client data update the blank server, or will the blank server wipe the clients clean? If this approach works, should I sync my clients with fresh/blank oC 10.0.4 and with Sqlite or MySQL?