Re-tested. And for sure, restore now works as expected. Got some messages while rebuilding the database for disaster recovery restore test:
duplicati-i174b98bbbd2f4cfcb449a4f1285818cd.dindex.zip.aes had invalid blocklists which could not be used. Consider deleting this index file and run repair to recreate it.
Unexpected changes caused by block duplicati-b278fddf65249422b85a22bf294342231.dblock.zip.aes
But all five backup sets which failed to restore earlier are now successfully restored. Without any other repair actions being taken meanwhile, or the backup destination being modified in anyway. I also used some of the older sets, I stored for debug reasons, when those were failing to restore.
I also did run the restore with and without parameter repair-force-block-use. It also worked as expected and practically seemed unnecessary now. On top of that I made just a few partial restores where most of data was already in the restore destination, but I just deleted / changed content of a few files and checked if state is correctly restored by restore process, and it is.
On top of that, many of the issues initially causing these problems with block and index files being left or missing due to bad transactionality and recovery have been fixed earlier.
Approved Finally
Issue ticked closed