Answer
Check the message's configured Receiver value against its actual media code — a Receiver value that doesn't correctly correspond to the specific media code actually being used, for example a Receiver meant for one connectivity type being used incorrectly alongside a different media code like MHS, produces exactly this kind of silent stuck-in-Released symptom with no visible error. Correct the Receiver to a value that genuinely matches the message's media code, and make sure that same Receiver is also properly registered, tied to the correct Site, under the 'Message Receiver' tab of the connectivity setup so it can actually pick up and process the queued messages. Note the process differs somewhat if the media code in use is INET_TRANS instead of MHS.