Clients Reporting to SEPM server are showing in Disabled Tab

Hi Experts 

Need your support to figure out the issue that we are experiencing in our envioment.

Since from yesterday most of the clinets are showing in disbaled tab. this is the 2nd time we are facing this issue in this month 

last time when we had this issue, we rebooted the server and made it work.but this time i need to figureout the cause 

one thing i noticed, we have 2000 K Seats but currently situation is under over deploymnet would that cause such issues ?

Please advice