A lot of problems. First year, Mk3 was good. Second with MMU2 not that bad, but now(MK3S / MMU2S) = bad
I use the lastest F/W and se a lot of bugs distubring Printing.
Load of filament fails almost everytime( even one load for single Printing). Its hard to get the printer to do anything cause almost every try fails.
It is not possible to use soluble filamnet at all. The filament get wind up inside the printer head each time, forcing me to a to much time fix each time.
The MMU2s 'bugs out' quite often and goes to somewhere around filament port 4/5, text in windows is loading filament 236 or something like this.
The first year was excellent, no problem at all. After the MMU2 arrived, I hade to put a lot of work to it, but it eventuellay did work ok.
After the MMU3S / MMU2S upgrade, I have a lot of problems. I do not have the time to put 200hours of tuning each time there un upgrade.
Not really happy at this time.
There might be more than one issue here.
In my case loading issues after some successful loadings had been caused by loosened screws on the MMU2s Idler barrel. You can certainly not go wrong if you check if the the barrel is screwed well to the motor axis without any play and slipping through.
I have not heard about the MMU selector going to random locations without actually another underlying problem. I would check with simple load actions from the MK3s menu. Load filaments 1-5 individually from the screen. Look if the selector moves to the right position, check if really the correct counter wheel is pressing down. Check if FINDA is registring the filament reliably. Maybe you need to clean out the FINDA channel from strings or such if it doesn't.
That also single filament loading into the nozzle fails seems to suggest that you do have an underyling issue. Does during loading the MMU ever engage in the fast loading step or is the filament loaded only in small steps fairly slowly?
PS: I just see that you have written that entry already some time ago, maybe you have figured the problem out yourself? If so, it would be interesting to know what it was.