Just a little heads-up.
I cleaned (again) the nozzle, with a grey filament to be able to see the black coming out. After almost ten pull-ups, I was able to have a clean grey filament, with no black. I then did a factory reset of the machine, leveled the bed, and reinserted the original black filament.
Here are a few pictures of what is happening at the moment. As you can see, some lines are missing. Seems like the filament struggles getting out of the nozzle, or alternatively, the feeder struggles to push it in, maybe because something blocks outside. I gave it a little help and pushed it manually, and it returned back to normal. The picture where there is no defect is actually taken later. For how long is it gonna print ok, I don't know. I'll keep you updated.
My parameters are default for PLA, with filament size at 1.68, flow at 120% (I noticed the lines didn't touch at the beginning) and temperature at 220 (to give it a little more fluidity).