I made the WASC listed on these forums. I have made it before with no problem. However,, tonight when I made it, it sank in the middle while I was baking. What could have caused this?

My oven temp was @325 degrees. I did bake a pan of cupcakes with it, and had to open the door a couple of times to check o them. Could that have been the problem? It was a fairly large round pan with 3" height.

Thanks!

Yes, opening the oven door too much can cause issues because you are dropping the oven temp.  May not be the culprit, in this case, but certainly could be.