It’s almost certainly to do with the timeouts not being long enough to allow for how much longer your packet is now taking to transmit.
The excel sheet linked here: DW1000 Power Calculator not working can be used to calculate the time taken to transmit a packet for a given set of settings and data length.
Increase the timeouts and receive to transmit delay times by the increase in packet length plus a little bit. Remember if it’s a round trip timeout (time between transmitting and receiving a reply) then increase it by double that since you need to allow for two packets to be sent in that time.