I have this one:
https://www.ebay.com.au/itm/VAG-COM-KKL-OBD2-USB-Cable-FTDI-FT232RL-Chip-2x2-Adapter-Cable-for-VCDS-Lite/283018196230?hash=item41e532f506:g:66oAAOSwdfZbK45b
Is your port selection in the tuner pro tools section set to the right port?
It automatically selects port 1, on my computers it shows up at com port 5 (Device manager, FTDI Device)
Are you correctly powering up the correct pins? My first attempts at bench flashing I had mirrored the port and got it all mixed up, but now its perfect.
Im actually using a Scangauge 2 plugged straight into my R - 1996 & running a 98 LPT ECU flashed with a 608 bin with no issues at all, Ive got it displaying RPM, Coolant temp, Voltage & another paramater I cant remember right now
Typically the scangauges dont work with the 850s, but it seems that using the newer computer has made it possible
What ECU do you have & whats been done to it?
Are you sure the 850 AWD LPT ECU is indeed M4.4?