I didn’t get an answer on this one, but had another issue which likely requires me to update (from 4.4.14.0 where I don’t see this issue) so ended up starting it to troubleshoot it on HL7800 intermittent KSUP:2 SIM NOT DETECTED - #13 by Antoine
Though to summarize, my MQTT server does receive the 2 bytes TCP data I sent and completes the disconnection [4.4.14.0 will return OK whereas 4.6.8.0 or 4.6.9.4 will return NO CARRIER]. The DTR remains low from start to finish of the MQTT transmission. I’ve tried the AT+TCPSTART? command however as per the HL7800 documentation, it just returns OK:
I am still hoping for a resolution on this issue as well, since it is preventing me from being able to upgrade modem firmware.