Lots of track updates (15hrs of work!) lost after an MB crash

[WimYogya]

An hour ago MB crashed (hanging, only option was to stop it) and I lost 15 hours of updates on numerous files. Mainly operas with detailed tracking/title and artist/singer information. All gone! And as you may know: entering classical music data in ANY player is always a very time consuming job - if you want to do it properly!!

How is this possible?
After each edit I saved all the new entries. But after the crash and restart all these tracks had their own information.
Then, if everything had been saved, why is it gone after a crash?
A file rescan did not bring back anything.

Is this a bug that started with MB3?
Never had it with MB2.

A few times before I noticed (in MB3) some strange (and possibly related) problems.
When updating multiple files (e.g. adding opera titles to the track names) things sometimes went wrong. The tracks seemed to have been DUPLICATED, two identical tracks with the updated titles. But... one was ok/active, the other was a dead link. Sometimes I could only verify the good ones by trying one by one. Sometimes the dead links had an exclamation mark in the front.

And maybe also related:
I created my own system to add classical performers to classical music. I used custom tabs as 'main vocalists', 'instrumentals', 'choir', 'orchestra'.
Upon my request MB adds all names automatically to a field called 'virtual performers'.
When done I use an ASR tool to copy the 'virtual performers' to the 'performers' field which is visible in the column brower field 'performers' on top of the main playing panel.
Result: if I select an opera or so, I see all the performers listed alphabetically in that field.
It works well.
But... after a crash as described before the structure is severely damaged: the virtual-performers/performers are listed properly. But in the individual track the individual fields 'vocalist', 'instrumentalist', 'choir' etc. are empty. The information is ONLY visible (in 1 long list) in the top 'performers' field, but not by there respective category.
How is this possible and how to avoid it?

One last issue:
In the past MB had (as I seem to remember) a rescan option saying 'rescan all files even if already in the library' (or something like that. Then a lengthy rescan process started, sometimes with beneficial results. Do I remember this well? If so, where is that option now? Gone? Why?

Any help?
Thanks!