When offering a filter in an interface based on an 'email' field including the 'Current User' this is case sensitive. If a user capitalizes a letter in their email address when signing up this possibly won't match exactly and the filter doesn't work as intended. The idea here is to make this filtering to be not case-sensitive.
I've seen this brought up several times here. Until this is resolved natively, workarounds (through helper formulas and automations) have been mentioned, too, you may want to have a quick search.
