Tried moving all resources from one resouce group to another one. Passed validation and started moving. This failed after 30 minutes or so but all of the resources are showing in the target resource group and none in the source group. System won't let me change any resources now. Throws an error saying that the resource group is being updated.
I left it for another 30 minutes but keeps giving the same error. Nothing in logs.
It's likely still in the moving process. The resource groups are locked during the move process. Were the VMs already stopped before the move commenced? You will probably have to just wait it out. I think it eventually times out after 4 hours!