You are not alone! Oddly enough, this is one area where ArchiCAD went backwards. I hostly liked the BimServer Manager for ArchiCAD 17 and before. It was a quick, dedicated app, not a slow web interface, and most importantly, it allowed multiple version modules to exist on the same server! This made the Migration a lot easier... the Users and Libraries were the same, and the Migrate Project tool actually WORKED! Why do they even offer Migration when the Libraries can't migrate, since they're not on the same server!
I haven't started migrating projects into ArchiCAD 20 yet, and I'm dreading the long nights I'm going to have to spend here. The web-based non-Java BimServer is NOT an improvement, and though I really thought they would work out the migration process, nothing has been improved.
It would be so much easier if we could, at least, Export and Import projects from the BS19 to BS20, and THEN let ArchiCAD perform the file migration. However, a wholesale upgrade tool would be best!
Since my office has about 50 users and 150 active BimServer projects (on 3 servers), I've had to give up some control and ask the Project Manager to migrate their own projects... at the risk of something getting screwed up. I still have to fix a lot of broken Libraries.
We are contemplating upgrading to the BimCloud, but there is limited benefit, and I haven't been able to justify the cost. We only have one office location. Though it would make managing Users and Libraries a little easier, it wouldn't fix the painful migration issues.
Phoenix, Arizona, USA
ArchiCAD 25 (since 4.5)
Macbook Pro 15" Touchbar OSX 10.15 Core i7 2.9GHz/16GB RAM/Radeon Pro560 4GB