That is kind of the same i have in my database.
https://forum.dxo.com/t/big-mess-in-database-with-new-version-and-old-version-installed/41150
I opened the same directory in V8 and later in V6 again, now my DB is messed up. Virtual copies over and over, 2 or 4 for each image.
Did not tried further until now, but this is really a bad upgrade path, to install it in parallel. I also did not found any documentation from DXO how exactly a upgrade from old to new version should be done.
The troubles started when i discovered that all my projects did not appear in the newer version…
Bruno