rak5010 uart_overflow

I am having an issue with UART_OVERFLOW errors on the RAK5010 comms with the BG96

You see at the end of the below commands the QNWINFO response from the BG96 is missing some characters. (But the issue happens in random places, not just there). If I slow the baud rate from 115200 to 19200 the problem pretty much goes away until I start using the BG96 to download a 22kb file from a server, then I get overflows again - although in this case it might be the 19200 is not fast enough to keep up.

Using the same code on a RAK8212 (which defaults to 115200) I dont get overflows (although I have not tried the file download on that)

In theory I have enabled the CTS control on the BG96 so with the commands below there should never be an overflow ? Any ideas ?

["AT+CSQ\r\n"
] "\r\n+CSQ: 19,99\r\n\r\nOK\r\n"
["AT+CEREG?\r\n"
] "\r\n+CEREG: 0,1\r\n\r\nOK\r\n"
Send to server
["AT+QHTTPCFG=\"contextid\",1\r\n"
] "\r\nOK\r\n"
["AT+QHTTPCFG=\"requestheader\",1\r\n"
] "\r\nOK\r\n"
["AT+QIACT?\r\n"
] "\r\nOK\r\n"
["AT+QICSGP=1,1,\"iot\",\"\",\"\",1\r\n"
] "\r\nOK\r\n"
["AT+QIACT=1\r\n"
] "\r\nOK\r"
["AT+QIACT?\r\n"
] "\n\r\n+QIACT: 1,1,1,\"10.34.15.70\"\r\n\r\nOK\r\n"
["AT+QIDNSCFG=1,\"8.8.8.8\",\"8.8.4.4\"\r\n"
] "\r\nOK\r"
Connected
["AT+QNWINFO\r\n"
New interpreter error: UART_OVERFLOW
] "NFO: \"CAT-NB1\",\"53001\",\"LTE BAND 28\",9554\r\n\r\nOK\r\n"