Module UART RX buffer

I cannot find information on the SPWFS01 UART RX buffer. How big is it? Since I have an issue when controlling the SPFWS01 from a host using UART. We have a cycle where we use HTTPREQ and in there use GET, PUT and then DELETE. Since the PUT also contains more headers and a body this message is a lot larger than the other ones but it is within the limits of my buffers (both HW and SW). However this AT+HTTPREQ with PUT works 49/50 times with the one erronous time being when the HOST is not able to transmit more than its first character. We are using HWFC and 38,4k.