first layer does not have an "infill".

@PriorityMotif You might have another (or an additional) thing to look at - there are little holes, which might be due to wet filament. This could also be the cause of the issue you are having - if the filament is too wet, it could cause partial blocking, which might create the thinning lines in the infill. This also would not be very visible in the perimeter.

If you hear pops during the print, then you have wet filament and, if that’s the case, I would suggest that you look into this first.

because the extruder slows down around corners.

Are you saying what we're seeing in the photo is supposed to be the same layer? Can you upload the exact gcode file you were using when printing, if you haven't solved it since posting this?

Download a profile from somewhere. No reason to start from scratch. There's a V2 profile on printable and they are functionally the same.

My experience of this is that is because Cura over extrudes the walls deliberately to help adhesion and strength - I want to say the setting is called "overlap". It's the one where the infil runs into the walls a little bit to tie together the edges, but that's always going to result in a bit more plastic being laid down in those areas.

Normally it causes a bit of a brim to cut off, but in your case it might just be enough to let it stick round the brim but nowhere else.

I read about the motor, I just wonder if the feed was doing something weird or there was a LOT of moisture in that roll (and I dont know if I ever saw it that bad. And I live in a place that seems to be soup in the summer time). It was just obvious popping, being that it was a new roll I still wonder wtf was going on that allowed the plastic to pop like that.