Very same issue, happening on two Ibi200+GV I own. I upgraded the firmware manually to the "latest" dated January 2018, V.3.2.1 Build 5794EX, but this morning I got the [!] in Obi Dashboard for one of my units for FW update, and I did it - resulting in Build 5757EX. Problem still persists.
I want to add: Ringing goes through, Caller ID is displayed, when receiver is picked up - CONNECT does not get to the SIP server, so GV does not know that receiver is picked up.
I also opened "Request for Service" ticket with Obihai, no response yet.
Seems like a problem is between Obi200 (PBX) and GV Server. The [CONNECT] is either not sent or not always received.