Is your SDDC in Northern Virginia? If so, there is currently an outage reported in effect: https://status.vmware-services.io/ While dated for Sept. 13th, it is still listed as active. Please engage support and inform them of your situation if this is still persisting.
No it was in the UK, it took over 1hr to get the new host in and VMs migrated. Not all VMs were powered up by HA which has a SR raised as to why. This was not reported as any outage on the support page for UK.
My main concern is all the disconnected VMs were ended up being powered off for such a long amount of time before HA kicked in and even then not all of them were automatically powered back up
VMware online support were clueless over the outage and i had to send screenshots as proof