Filter - Greyed Out!

I'm trying to filter a long list of files but the filter dialog box is greyed out and doesn't allow any text entry! Any Ideas? I'm on a Mac if that makes any difference.
Thanks in advance

Can you show a screenshot of what you're describing?

same issue:

version 1.7.5 (76)

Can you please update to the latest version 1.8.11 and see if the issue persists?