After a lot of pressing I finally got an update on this issue.
"This is happening due to a rare condition in the VCenter HA service. This is a known issue by engineering, and currently, there is no resolution. The engineering case is 2802103 for your reference. You can clear the alarm by disabling and enabling VCenter HA as a workaround."
The engineering case is open since 17/06/2021 and was first noticed in 6.7 P04 and is still happening in 8.0.
A VM deletion seems to trigger the event.
Unfortunately we are still stuck with disabling and enabling vSphere HA to resolve.