training self-supervised conformer
Hi, I use `examples/asr/speech_pretraining/speech_pre_training.py` code to train a self-supervised using conformer on my custom dataset. I just changed the manifest files address in conf file. When I run the code, I encounter the below issue.
I use NeMo version 1.8.0. Also I test it on version 1.9.0 but the same problem occured.

**Environment details:**
torch 1.9.0a0+c3d40fd
pytorch-lightning 1.6.4
Python 3.8.10
NeMo 1.8.0

![Screenshot from 2022-06-07 14-22-48](https://user-images.githubusercontent.com/105767588/172352592-ed10430a-6e29-4723-a6e9-d9b7d96316d8.png)

