Oh my, what a shame, they were beautiful! Was your batter still cold when you piped it or had it warmed up? I had that happen once when i didnt soap cold enough, now i know to keep the ingrdients cold cold, like 60 degrees or less. Back then though i thought you just got a heavy trace and then piped. I feel your pain and remember the disapointment.
I remade them on Thursday. I popped them in the freezer for 24 hours. I pulled them out yesterday....they started to overheat again! I used the same batter for the top and bottom....the only difference being the addition of cocoa powder the the bottom batter. The bottom seems to be whats overheating. I put them back in the freezer. I was blown away that they attempted to gel and overheat after 24 hours in the freezer.
Every soap I put in freezer reheats 24 hours later once pulling it out. I leave it in fridge another 6-8 hours to prevent this.
Freezer can slow saponification so much so, it really wasn't happening. Pulling it out to room temp speeds it back up and causes it to actually heat right back up. So if you throw it into the fridge after a day in the freezer, it will allow it to warm just slightly enough to finish off saponification, but not allow the temps to raise to the point it otherwise would in room temp conditions.