?
There have not been any updates that would have impacted this recently, or known issues like this. Unfortunately, there are a lot of things that can cause this, but one of the most common ones is one or more agents with a bad network connection.
Because agent communication is pooled, and I/O is a bottleneck, often time one server is waiting for another to finish, sometime it can be difficult to tell which specific agents are causing the problem.
The easiest way to find problem agents is this...
Stop the BuildMaster service from the Web UI, then Start it
You will see a bunch of "AgentUpdaterChecks" running simultaneously
These should take seconds at most to complete
Try to identify ones that are taking too long
Once you've found agents that never seem to complete the check, stop the service, then disable those servers (Edit Server > Active)
Go back to the beginning
Once you isolate the servers, it should be relatively easy to find them out.