I have a new 5.7.2 wdm server on Windows 2012 R2 and about 1000 thin clients which have all been freshly imaged. All 5010 models. They all successfully registered in wdm, but now after several days, about half of them have stopped checking in and are showing as offline in wdm. Spot checking shows that some simply cannot register after reboot and some are showing registered, but are still offline in wdm and some are legitimately offline. There are no apparent connectivity issues from the clients to the wdm server. wdm server health is all green.

I've googled it to death and can't find anything which might be causing this. Any ideas?