Why is filament building up on the nozzle during a print?  

RE: Why is filament building up on the nozzle during a print?

Looking good!

RE: Why is filament building up on the nozzle during a print?

For your info if you ever need to remove the nozzle. Do a cold pull first, this will make life easier.

https://help.prusa3d.com/article/lnbcnhg76k-cold-pull

Slight difference is depending on the PLA you use, you may need to allow the temperature to drop to 80, the easy way, bring it up to temperature to melt the PLA, extrude some, open the filament door, press reset on the printer LCD panel and once rebooted, just watch the temperature drop, but push the filament gently until about 180 degrees, pushing after that won't make any difference.

Once the temperature drops to 80, pull the filament out the top of the extruder.

If you shine a torch down at the bottom of the nozzle, you should see the light straight through down through the printer when looking from above.

Don't try this with PETG, you will end up picking up your whole printer! - I found out the hard way.

Then heat the print head back up to 280 Deg, switch of the printer (You don't want to accidentally short anything) then quickly holding the heater block with the correct sized open ended spanner or a small adjustable spanner, unscrew the nozzle with the correct sized spanner for the nozzle.

You should then have an empty nozzle, free from filament.

Refit cold, jus nipping up gently, bring up to 280 Deg C heat then carry out final tightening again power off, hold the heater block and tighten the nozzle, but not too much, there should only really be the smallest of movement, I cant think of anything to compare how much force, but probably no more than the force required to open a new tube of toothpaste, it's not excessive, but just firm enough, if you are struggling to tighten it, then you are probably over tightening it.