Thanks for following up.

Anecdotally it's now much better. I mostly care about png at 200dpi and after a 100+ attempts haven't hit any problems with it. But that's not really a big sample. I'm trying unrepresentatively short formulas (1-2 letters) because I've had luck finding problems with those, but also because they're fastest to try in the editor ;-)

But I have found one oversized gif: http://latex.codecogs.com/gif.latex?%5Cdpi%7B200%7D%20c

and one oversized and inverted png at 300dpi: https://latex.codecogs.com/png.latex?%5Cdpi%7B300%7D%20p

so it's not 100% fixed yet...