Ricky, did you add any water to the compound to make it a little thinner?
With the high iron content in Toronto area water, I find this does happen from time to time.
Prime the walls with Zinzer stain blocker, then repaint. Problem will be gone.
regards
John
Yes! I did a final skim coat and the premixed was too thick.
Ok. I'll repaint it one day. For now, the snakes don't mind the yellow.