Hey, it started when I tried a new filament (Maths PLA+) (back to using my same filament I always use (Overture PLA), but it didn't remove the problems)

it was badly under extruding, the extruder was both skipping & sliding, and even pushing by hand was much harder than it should be. I ended up putting a new nozzle on it, looked over everything else, and on the surface everything looks fine, but still under-extruding.
now I noticed where the rest of the filament has gone: (squeezing out above the heater block)

3dPrint.jpg

I noticed that bottom heater block was extremely loose, and I don't see a way of tightening it up...

any ideas?