Dual Extrusion issues

[earthcaretech]

Hi
I've been having difficulties in getting dual extrusion prints to work.
I have a Formbot T-Rex 2+, and using the left (main) extruder seems to work fine. But after one successful print with both extruders (2 different materials), I had extruder collisions. I updated the printer firmware, which seemed to resolve that issue, but has introduced two more, and I can't tell if it's the printer or S3D.
Every time I start/restart either, I have to use S3D's configuration assistant to ID the printer, otherwise it simply wion't connect over USB. When it does connect, and I set up and send a job, one of the extruders (the right one) fails to heat up; sometimes the left one heats up to around 80% of the set temperature, and then heating fails altogether with a warning on the printer screen.
I'm wondering whether anyone has seen this issue, and/or knows how to solve it?
Thanks
Edwin