When you’ve been backing up your vCenter Server Appliance via the built in backup feature in the admin UI, then come to initiate a restore to new vCenter server. Make sure it’s the correct version, selected the same size (medium) and then ended up with a bunch of failures. The errors weren’t very helpful to be honest

The errors:

Error Backup detailsMetadata and system validation failed.
Error: Unknown system resource type seat

Error: Unknown system resource type vtsdb
Error: Unknown system resource type Iv_Ivm_snapshot

Check the resources of your vCenter appliance VM! this is what caused me the problem. The disk size had been increased from default.

Example of the disks on my standard vCenter server:

What we did was compare the old vCenter appliance disk sizes and make those match the newly deployed vCenter appliance (edit the settings of the VM power down)

Without doing anything else, just powering back on the VM and running the restore again from where the error was displayed this fixed the problem.