When I put a call on Hold, this call drop after 1.4 minutes on hold. Looking the capture the UCM sent the Bye to the carrier.
Did you get your nats right on the firewall?
put public ip on the UCM nat?
In the “SIP Settings (ToS)” section there is a “RTP on-Hold Timeout” which is by default 90sec if my memory serves right. Increase it or you can leave it blank (blank means no timeout.)
Check RTP timeout and RTP hold timeout in PBX settings, SIP Settings, TOS. Look for the one with 90 seconds and increase.