Moving to Needs Discussion to determine the course(s) of action:
Impact: Users in the control group in wikis where there are no copyedit and (unstructured) link tasks will see an empty filter but all possible tasks are in the feed.
Possible actions (from @Tgr's comment in the original task)

• Fallback chain of default task types
• Allow the default task types to be configured via community configuration

After checking T294518: Add Image: Allow disabling feature via community configuration and to add more on the following use case, I added the description of the current behavior:

You'll end up with an empty task filter list but lots of tasks in your feed.

Similar error happens if a user does have prior task type settings but those task types don't exist anymore.

(1) The task types filters (after disabling some tasks on Special:EditGrowthConfig) would not display any pre-selected task types. A user would be facing with un-selected tasks types filters.

Users should either see new default task types selected or be forced/warned to select new task types.

(2) The first SE card would be loaded. The right hand navigation (the arrows) would look active, but if a user clicks on the navigation arrow, the incorrect counter and the warning would be displayed: