If it's just oozing out and not printing the priming line, then it's likely the filament sensor's not triggered... The MMU and extruder are both feeding it through.

Pure speculation, of course, as I've not had that problem. But it fits the observed facts. 

I am not sure that the filament sensor has to do with the first layer success.  

Indeed. The PINDA is designed to detect the bed. The filament sensor, on the other hand, is designed to detect filament.

The manual says to roughly align the PINDA with a tie-wrap, and the filament sensor with an Allen key. I'd suggest that's all good, but for a final check of the filament sensor; use actual filament.

The sensor is made to detect the bed and not filament.  

The manual says to use the Allen key for calibrating the filament sensor, but I've found using some actual filament is better. If nothing else, it's what the sensor's designed to detect after all. It's also worth remembering that the 'chimney' will move around a bit as you tighten up the screws. It'll also creep over time. So it's always worth unhooking the coupler at the extruder end and sticking a bit of filament in a few times as you check the sensor info. (I got for 10 / 10 on that check.)

Yeah, just fixed the IR sensor now and its appears to have solved the problem, however I'm starting to notice issues with consistency so now for trying to troubleshoot some other issues for me haha

I've been having the same problem, but I have calibrated the IR sensor a few times, don't see anything funny  but it doesn't make a difference.. have you figured anything out?

thank you