Today I tried the Center/Radius filter on both "Hidden date" and "Hidden month" map pages. This filter has worked correctly in the past.
On both pages; entering "London, ON, Canada" returns ZERO results and message "No caches found with the selected criterias.".
I found that "London, London, ON, Canada" works; but I cannot find similar workaround that works for other cities. The following cites do NOT work:
Salt Lake City, UT, USA
Colorado Springs, CO, USA
Try these two links (D/T Matrix page) for example ...
London, London works