Recent migrations have been flying through but today (to a different DB) its not good.
All of the mailbox move requests are stuck in a status of Relinquished or RelinquishedWlmStall.
Looing at move request statistics it seems it its saying:-
"Job is waiting for resource reservation. MRS will continue trying to pick up this request. Resource reservtion failed for DB-XYZ. Load ration 999999. Load state "critical". This resource is currently unhealthy.
Servers look fine. No other problems.
Just migrating to a different DB.