Do these steps succede?
1. Storage - File Servers -> Refresh
2. Repositories -> Refresh
3. Server -> Rescan Physical Disks
4. Server -> Rediscover Server
These steps do succeed individually but don't help be reclaim the VMs.
If you take a look at the console of your OVM servers, they should print the former UUID on the screen right below the local hostname. If the screen is blanked, hit the shift key. The manager UUID is usually printed on the "splash screen" of any of my OVM servers...
Also, if you print the contents of this file on any of your OVMS: /etc/ovs-agent/db/server, you will find something like this:
My UUID is actually 0004fb00000100007e451289f3bead2f, go figure…