I enabled mod_expires on my staging server and my apache/NGINX configuration still works. On centos 7.2, plesk 12.5.30, Hetzner.
Do your websites run when NGINX is uninstalled?
Kingsley's solution could work. I had the same issue after an automatic upgrade to 12.5.30. I looked at Fail2Ban logs and found that my NAT ip was banned around the same time as the upgrade (plesk-apache-badbot jail). Made it a trusted ip and have had no problems since.