Originally Posted by Saddlebag
I suspect it closed off and wasn't completely cleared up. Try soaking twice daily with Epsom salts for a few more days. The surface of an abcess can close over when it hasn't healed inside, creating a perfect medium to flare up.
^^^ This. Last year my horse got an abscess that did the same thing. It finally cleared up when I soaked & wrapped his foot every day for 10 days, even though he stopped limping after 2 or 3 days.