If our server needs a restart during the day, if we attempt to load NM
just after the restart then the system starts to crawl to a halt.

The console shows requests going up. And then pendig requests start to go
up too.

But Users can't log back in, it says server not responding.

The server utilisation get's high, and becomes sluggish.

If I am lucky I can shutdown gracefully.

If I leave the server for a few hours ( usualy untill all the clients have
been rebooted ) it will start ok.