Warp Speed

Warping on the corner of the first floor piece.
The other two pieces are fine.

I'm getting warping of some pieces from my 3d printer again, as I did when I first got it about this time last year.

There are a number of variables that could be the cause:

1. Inconsistent heating across the bed
2. Change to a new variety of PLA filament
3. Seasonal drop in ambient temperature, and an air current across that bit of the bed
4. Angry gremlins

It always seems to be in things printed on the front-right corner of the bed, so I suspect either or both of (a) or (c), but I'm not discounting (d).