Trying to copy an existing closed change and fill in the required fields and save it, the screen freezes and nothing happens.
Doesn't create a new Change request.
Custom "Copy Change" UI action.
The "Copy Change" UI action showing on change request form was not OOTB.
Reverting the action to OOTB did fix the issue.
Custom UI action was generating aN URL with different parameters than OOTB which the form couldn't process and submit.