Unable to start a VM with a Shared Disk

Pretty old thread here: https://social.technet.microsoft.com/Forums/en-US/ec1c6756-7890-419a-89d0-cf7570901549/error-synthetic-scsi-controller-failed-to-power-on-the-process-cant-access-file-because-being?forum=winserverhyperv It states that the host should be rebooted and you can try to reattach VHDS to the VMs.

Alternatively, you can try building guest failover cluster using iSCSI LUNs. As an example, StarWind VSAN can be used. https://www.starwindsoftware.com/resource-library/starwind-virtual-san-for-hyper-v-2-node-hyperconverged-scenario-with-windows-server-2016/