Creating and scheduling a worker task for Always On Availability Groups failed due to lack of resources (SQL OS error %1!s!). ...

Creating and scheduling a worker task for Always On Availability Groups failed due to lack of resources (SQL OS error %1!s!).   Processing of new actions might be delayed or stalled until the resource limits are resolved. Reduce the memory or thread count on the instance of SQL Server to allow new threads to get scheduled.  If new tasks are scheduled the problem might resolve itself. However, if the problem persists, you might need to restart the local instance of SQL Server.