lightning == 2.1.0 crashes while loading existing models

As of now, we are pinning lighting to a lower version (2.0.9post0), but we may need to investigate this further if issues persist.

The error output relates to using class instead of instance of pytorch modules to load pre-existing weights. Strangely, the object which calls the relevant load_from_checkpoing() method is an instance, so we current don't understand why the problem happens.