[V17] - tracking_manager Is not showing many2many field changes properly

[Marrieta99]

Module

tracking_manager

Describe the bug

Once tracking_manager is installed in my database, relational field changes in every model are shown as "None -> None" regardless of what change was made

To Reproduce

Affected versions:
V17

Steps to reproduce the behavior:

1. Install tracking_manager module.
2. Modify a many2many field that is tracked by default (model does not even have active_custom_tracking set)
3. Field changes are shown like this in the chatter
   
4. This also happens with models that have active_custom_tracking set as True. Previous or current values of tracked many2many fields don't show.

Expected behavior
Previous and current value of the field should be displayed, as shown here

Additional context
I have encountered this issue in te V17 enterprise version