KeyError on editing Filter collections

[dolsysmith]

Clicking Edit for a Filter/Sample collection causes a KeyError. Functionality is not impaired, but the error appears in the logs:

Traceback (most recent call last):
File "/usr/local/lib/python3.8/site-packages/django/forms/forms.py", line 163, in __getitem__
field = self.fields[name]
KeyError: 'schedule_minutes'
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/usr/local/lib/python3.8/site-packages/crispy_forms/utils.py", line 70, in render_field
bound_field = form[field]
File "/usr/local/lib/python3.8/site-packages/django/forms/forms.py", line 165, in __getitem__
raise KeyError(
KeyError: "Key 'schedule_minutes' not found in 'CollectionTwitterFilterForm'. Choices are: collection_set, credential, description, end_date, history_note, link, name, visibility."

Confirmed that this issue is present in prod (so not caused by the upgrade to Django 3.2).

scheduled_minutes is set to be excluded in CollectionTwitterFilterForm, etc., per the Django documentation, so I'm not sure what's triggering the error.