Does anyone have suggestions for sniffing a Kess KWP protocol flash on CAN high/low wires?

Normally, I plug a k+dcan cable into a Y splitter cable and listen live with putty or some other serial logger.

However with the Kess, when I plug my K+dcan cable in the OBD Y splitter, there is packet loss whether i'm listening live or not. It shows as either unable to identify ECU or or it identifies it with bad data ie VIN and HW ID appear truncated. The sniffed data is accurate up until the failure too.

I have both a genuine and non kess both of which behave the same in this scenario.