This happens from time to time. it mostly happens on the first layer after some infill.
Is this under extrusion? if so, what can I do to helt it? if not, what is it then?
The outher (and inner) surface looks good, there are no string, no deposits from oozing, I don't think there are any problems other than this, and it bothers me.
I had one time where the printer was printing in the air, this was due to a knot on the filament, but can this still course problems? because of the knot, the drive wheel was dirty, so I cleaned it, thus there should be no problem there.
The printer have (only) been running for a week, if that have anything to say..