on_epoch logging in validation_step appears to miss the data for the 1st epoch: Lightning 1.0.3
🐛 Bug

On_epoch logging in validation_step appears to miss the data for the 1st epoch. My epoch has 313 steps and therefore I expect the first on_epoch logging in validation_step should at step 312 (0-indexed), but I saw it was at step 625, the end of the 2nd epochs.
Please reproduce using the BoringModel and post here

To Reproduce

I have 4 GPUs and used DDP and the following validation_step:
def validation_step(batch, batch_idx):
    loss = self.forward(batch)
    self.log('loss/valid', loss, on_epoch=True, on_step=False, sync_dist=True, sync_dist__op='mean'

Expected behavior
The first on_epoch logging should occur at the end of the first epoch, not the second.

Environment
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Colab Notebook: Please copy and paste the output from our environment collection script (or fill out the checklist below manually).


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wget https://raw.githubusercontent.com/PyTorchLightning/pytorch-lightning/master/tests/collect_env_details.py
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python collect_env_details.py


PyTorch Version (e.g., 1.0):  1.4
OS (e.g., Linux):  Linux
How you installed PyTorch (conda, pip, source):   pip
Build command you used (if compiling from source):
Python version:  3.7
CUDA/cuDNN version:   10.1
GPU models and configuration:
Any other relevant information:   PyTorch Lightning 1.0.3, 4 GPUs with DDP

Additional context