I don’t see anything obvious that could be causing this, but I will continue to look into it. In the meantime, the couple of similar forum posts I could find were solved by increasing the MQTT packet size. If you have already done this, great! We can eliminate it as a possibility. If you have not, I would recommend giving it a try as it is a silent refusal by the underlying the library if the packet is too large.
I will continue testing and see what I can find.
Thanks!
Julia