We have a UCCE call center that has a challenging workflow. The agents take inbound calls to their ACD lines, then from that line, they will make an outbound call to a doc's cell phone. If the doc answers, they conference the calls together and all is well. If the doc does not answer, they will leave their private number for call back. When the doc calls back, they are currently parking that call, then going back to the ACD line and conferencing in the parked call.
If they try to conference using the "Active Calls" feature while on an active ACD call, the agent state will stick at "On Hold" and when the call is completed, the phone must be restarted to release the agent from that state.
If they try to conference using "Active Calls" while on a non ACD line and conference in an ACD call, the agent state sticks at "On Hold" but will release back to Ready when the call is complete. This would skew their CUIC reporting.
Finesse 11.6 (stock w/Live Data)
"the phone must be restarted to release the agent from that state." sounds to be an issue to me. I would suggest opening a TAC case for that.
Other than the above, is your issue the fact that the agent state is stuck in "On hold"?
If an agent is actively on a call, they should never be in "hold" state. The only time they should ever be in hold is when they have calls but are in "hold" state for each one. From your description, it doesn't sound like that is the case, so I would definitely go up the TAC route.