I had an issue with an early build of 14.2 where the Workgroup agents would be on permanent wrap-up and never receive a call. Looking at my email messages, it looks like this was fixed in build 19.42.6503.0.

The Call Communicator did not show anything was wrong with the agent. I ran the workgroup CLI tool to see that the agents were in wrap-up.

But as soon as one issue was fixed with an upgrade, another issue came up. Right after the upgrade the voicemail escalations stopped working.

You may have to check the Shoretel release notes to see if this issue was already fixed in a later build.

Searching through the Fixed issues I found:
Known issues fixed in ShoreTel 14.2 build 19.46.7601.0:
ENG-368800 Calls to workgroup agent cannot be answered

Known issues fixed in ShoreTel 14.2 build 19.45.8701.0:
ENG-327956 Workgroup Agent's phones when logged in are not getting calls
ENG-252141 Workgroup Agent goes unavailable for Workgroup calls even though they are idle
Known issues fixed in ShoreTel 14.2 build 19.44.2503.0:
ENG-180322 Unable to answer Workgroup calls