If suddenly your WordPress site that uses Wordfence starts throwing errors upon logging in that look like:
Warning: A non-numeric value encountered in [path]/wp-content/plugins/wordfence/lib/wfUtils.php on line 1664
Warning: A non-numeric value encountered in [path]/wp-includes/functions.php on line 74
I have a potential solution for you! There seems to be a problem with the way the Time Zone was stored, when you go to Settings –> General in WordPress, mine was showing UTC+0 but I also saw these non-numeric errors on that page. I re-set my timezone and save the settings… the errors on the page went away and logging in works as expected now.
Original source of this solution was this post on WordPress Support as answered by @wfadam: