Lightroom: Several images (not all) are slightly or heavily turned after rendering.

Take a look at each image in the develop module:

If you look at the rotation angle in your Crop dialog, does it show a value?
If you look at the rotation in your Lens Correction Panel, does it show a value?

All values are zero.

I would be betting on something messed up with the Lens Correction Panel settings. The fact that it shows you outside the boundaries of the rotated photo is the clue.

What happens if you hit reset on the image? Does it straighten back up?

I guess I found the problem. When importing I had the AUTO button active as a standard to correct geometric distortions. I very much believe that's the problem after reimporting without the button active.