Dot-walking doesn't seem to be working for Tags filter option on Assignment Group => Group Fields on incidents.
Somehow only the Incident table tags are recognised even if the filter option is set on Assignment Group.Tags.

1. Navigate Tags on Navigator filter
2. Click System Definition> Tags
3. Click New button 
4. Fill the Name filed and click the submit button.
5. Navigate core_company.list on Navigator filter
6. Open a record and add the tag you created from More option button.
7. Navigate task.list on Navigator filter
8. In the list that appears, click the filter icon and, with the "Show related fields" option enabled in the dropdown
9. Select Company => Company fields and then navigate to Tags
10. In the "Select label" field, enter the tag you created in step 4 above.
11. Click Run

Expected Behavior: 1 record should be shown

Actual Behavior: The list is empty

After carefully considering the severity and frequency of the issue, and risk of attempting a fix, it has been decided not to address this issue. We do not make this decision lightly, and we apologize for any inconvenience. If you have any questions regarding this problem, contact ServiceNow Customer Support.