we struggled with this, there was no obvious reason, it seemed fine on other sites, we dropped the wf tables, reinstalled. eventually we discovered the only fix was to revert to wordfence 7.3.6 via the link at the bottom of https://wordpress.org/plugins/wordfence/advanced/ and ensuring we disable wordfence autoupdates – we are php 5.4 – will be looking at upgradged php and our server in due course but this was our only workaround
i would also like to know about an update on this issue
