Hi Andrew,
Thank you for your reply.
A colleague reported it to me shortly after Revive was upgraded via cPanel >> Softaculous Apps Installer >> Upgrade to 5.0.4
Before that Revive was fully functional and we were able to delete Advertisers.
As far as I am aware MySQL hasn't been updated or changed, although php has been upgraded.
Current versions are:
PHP Version
5.6.40
MySQL Version
5.7.29