I called up and the Australian distributor said they won't touch anything that wasn't purchased through them and I'd have to deal with the person I purchased it from. It's not unusual for Australian distributors to have this attitude.
I also started having the 12th fader start jumping around erratically intermittently at a gig on the weekend, which was very frustrating for me.
But, after chatting with Matthias Hinrichs directly
We appear to have resolved the issues I was having!
The touch strips rely on pressure to get readings
if the screws in the underside are too tight, it pulls the top layer of the case down onto the strips and you can get bad readings (including unresponsive faders or intermittent erratic values).
So, my unit is repaired and fully operational and it just took some tinkering with a screwdriver.
I can replicate the fault by tightening any of the middle rows of screws on the back of the unit and fix it again by loosening them.
I'm really impressed with the level of customer support with this product!
We complained in the M-Series users facebook group that we weren't happy and that prompted the product manager of the company to directly message us to see if he could help (including offering to send us a new unit if the troubleshooting tips didn't work). Together we were able to get to the bottom of this and that should help any future users if they encounter this kind of thing themselves.
I also wasn't aware of the Console Tester application under Menu>System>Tools. Which is super valuable for seeing what information a control surface is sending to your computer. If you're having issues I recommend utilising this program to help you see what is going on.
So yeah, if faders don't respond properly, try loosening the nearest screw on the back of the unit and see if that helps. I was having similar issues with a friend's M-touch at the same gig, when I'm next able to borrow it, I'll try the same trick and report back.
Anyways. Thank you Matthias!