In the past few days I've run into multiple issues with my Enterprise system. The most recent issue is that the ArcGIS Data Stores that are registered with the server no longer appear to be connecting, and as a result all of our map services are devoid of data. This is a completely new problem for us, as I was able to consume the services as recently as yesterday.
The only change that has been made to the Enterprise system is that the ArcGIS Server Security 2020 Update 1 Patch was installed, but the version was kept the same (v.10.5.1). Is it possible that the patch is causing the issue? Or should I be looking for other causes?
Turns out there's not an issue with the data store, there were hundreds of ArcSOC.exe processes hung on my ArcGIS Server machine causing the whole system to bog down. I restarted ArcGIS Server and did a hard reboot of the physical machine and it seems to have cleared up the issue for now.