The 'Manually applying rules' function does not work.

Since updating to version 10.3.1720, I have been unable to manually apply rules to existing emails. For example, after creating a new spam filter, I want to manually test it. Filters do work for incoming emails, but not if selected manually.

It is possible to select the option, but the pop-up screen remains empty, showing only the loading icon.
Can anyone else confirm this issue, or do I need to try reinstalling?

Thanks for any advice!
Steff