In the end, I resorted to breaking the cluster and then mounting the LUNs. Most of the VMs I kept on one server, but I wanted to move a handful to what used to be the other node of the cluster. However, when reassigning the LUN in the MD Client to another host, I received an error that there was already a persistent reservation on the volume and that I should talk to my administrator.
In order to free the SCSI-3 reservation on the LUN, I had to run this command:
After that, I was able to successfully re-assign the LUN.