BG96 dead after TCP send

I have a device using the BG96-MA (firmware BG96MAR03A05M1GA). My firmware is working very well normally, it opens a TCP socket, sends some data, reads a response and closes the socket. However, there have been two instances on two different modems where a certain message (not the same) has caused the BG96 to stop responding to any commands.

I have captured this with an oscilloscope:

> AT+QIOPEN=1,0,"TCP","url-redacted",1234
< OK
< +QIOPEN: 0,0
> AT+QISEND=0,517
< >
send lots of data
< SEND OK
> AT+QISEND=0,0
nothing after 120 seconds, no response to any command after this (tried AT+QIRD and AT+QISTATE).

Normally the AT+QISEND command responds immediately.
I have the device with this modem and can reproduce this behaviour. If a different message is sent the modem works fine, so it seems to be somehow related to the contents being sent.

Any help would be much appreciated.

Also worth noting, the server successfully receives the message and sends it’s response.

I used a different modem to send the exact same payload and it worked fine.

I modified my firmware to send the TCP payload in 50 byte chunks and that avoids the problem. I don’t see why that should make any difference, the command is supposed to accept up to 1460 bytes and even responds with “SEND OK”.

You means after updating the firmware that the problem is resolved?