This is very strange, and I think it is a new bug in Lightroom Classic 8.0 (build 1193777), or perhaps it is something particular to my computer.
If I take a bunch of photos with the same value of either Location (= Sublocation), City, State or Country, select them all in Grid view, and clear that field (Location, City, State, or Country), the metadata filter bar does not update with the new values.
For instance, if I have 4 photos with City = "San Francisco" and I clear that field, the field changes in the inspector panel, but the number of photos with City = "San Francisco" does not change in the metadata filter panel.
This only happens when I clear the fields Location, City, State or Country. If I clear, e.g., Creator, it works correctly, and if I change Location/City/State/Country to a different value (even a single space), it also works correctly.
I haven't found a work-around. Optimizing the catalog doesn't change the values in the metadata filter panel, nor does closing the database and reopening it.
Do other people see this bug, or is it something specific to my setup (in which case I'll do further testing)?
Adobe has acknowledged this bug. Please add details of your issue, including the first ten lines from Help > System Info, to the bug report: Lightroom Classic: Library Filter using Location Metadata does not reflect removed location metadata | Photoshop Family … Be sure to click Me Too and Follow in the upper-right corner. This will make it a little more likely Adobe will prioritize a fix (just because they acknowledge a bug doesn't mean they'll fix it). And you'll be notified when the bug's status changes.