Difference between the checkpoint val_cer and real val_cer on the validation set

I am using stratedy=ddp and saving checkpoints by using the appropriate class named ModelCheckpoint which I pass to the trainer with the argument callbacks.

The checkpoint saved is for example epoch=204-val_cer=0.0459-val_loss=1.1404.ckpt as I set to put there the data of validation cer and validation loss. However, when I run the checkpoint with the validation set the validation cer is different (using the same batch size and number of gpus as what was used during training).

If I see the tensorboard logs they agree with the validation cer displayed in the checkpoint name.
The cer is implemented through the torchmetrics.CharErrorRate() implementation.

So, what am I doing wrong?

Here, I report the code for the checkpoint:

checkpoint_callback_val_cer = ModelCheckpoint(