Loss of accuracy when saving in H5 format

Greetings to the whole community

Why is accuracy lost in a model based on the EfficientNetB0 architecture when saved in H5 format ?

I am doing some experiments training classification models from different architectures for mobile devices (MobileNet, NASNetMobile and EfficientNet) and by storing them in H5 format the only model that loses significantly decreases its accuracy are the models based on EfficientNet.

When entering a model based on EfficientNet and evaluating the accuracy, values in excess of 96% are obtained, but when saving the model in H5 format and testing again with the same dataset, the accuracy is reduced by up to 30% (obtaining an accuracy ranging between 66% and 69%).

Does anyone know why this is happening ?