Could be any number of things really;
Did you carb count for the food and if so, did you calculate the amount correctly?
Could you possibly be unwell/becoming unwell?
Is your insulin pump site inserted correctly? (Even if it was working well previously, even a minor knock could dislodge it)
Is your insulin in date?
Could your insulin have gone bad in the pump?
I could make a very, very long list of all the things that could have happened, or it could have been one of those weird things that happened for "no reason" at all. My first port of call if I'm going above 20 and I've already given insulin that doesn't seem to be working after a couple of hours is to replace my entire insulin pump set (insulin included).