Third layer epic infill failure  

Third layer epic infill failure

I was printing a case, the parts depicted in these images are the first few bottom layers, which are effectively a flat sqaure. This is a PETG print using 0.3mm layer height. I've printed many boxes of similar size and shape, in the same material, with the same settings. The first two layers were fine, then this happened on the third layer:

I thought maybe it was an issue with the material, so I reprinted in orange, and the same thing happened in exactly the same place. I let it go long enough to do the fourth layer so I could see if a layer shift had occurred (it hadn't; perimeters on the fourth layer were fine):

The infill appeared to be offset a bit from the edge, which I just don't get what happened. You can see a little bit of a gap in the above picture. It happened in both the X and the Y axis. Maybe what happened was that it was getting lifted right at the end and dumped somewhere else. To add insult to injury, here's what my silicone sock looked like afterward:

That's only a portion of the PETG that I cleaned off of the hotend. There was more. Orange PETG had oozed between all five edges of the sock and the hotend. My working theory is that the sock was either dragging on the print, or had slipped just off the tip for a portion of the PETG to get trapped inside the sock. I'm just not sure why this only happened on the third layer (first and second layers were fine, on both prints) and I'm not sure whether the fouled up sock was the cause, or a symptom of something else that went wrong.

I'm now doing a third print, without a sock, to see what happens. In the meantime (it'll be an hour and a half before we get to that problem layer) has anyone else had an infill issue like this before?