I have been tackling a issue for some days now, and i was able to pin point in what exact situation it occurs.
Every time there is an extrusion for a Gap fill just before a perimeter start, i get a blob on the start of the perimeter that also translates most of the time to a unveven line of extrusion.
I have tried this with SuperSlicer (2.4.58.5 and 2.5.59.0), tried with PrusaSlicer also.
Im not completely sure if this is a problem with the Slicer, firmware or printer configuration.
I think printer configuration might not be as i would have the same problem elsewhere.
I found also that the line width was too big in some case and tried to reduce it, but it sill shows.
Only thing that completely eliminates it is turning off gap fill. If that is off i get a seam that is very good and no blob.
Tried with both normal Gap Fill and Arachne, in both cases the blob/ungly start layer is present.