I'm assuming this is a classification task as you mentioned accuracy:
100% on the validation set is usually a red-flag. Check there is no data leakage in your code (inspect it at each line). Make sure your validation set has a mixture of both classes (for example: is this a very imbalanced set and your validation set has all negative class?).
There is really no way to tell if or what the problem is without some description of the data or presence of code - but 100% accuracy is usually a big indication to dig into the details to find out if there's a bias you are adding to the system.