В репозитории вэбка старая, а сервер новый. Так бывает?
ВОТ:
On stretch, jessie, xenial and trusty distributions, PHP 7.2 dependency is not available, and therefore Zabbix frontend 5.0 or newer cannot be easily installed. Considering this, zabbix-frontend-php package has been replaced with zabbix-frontend-php-deprecated package on aforementioned distributions.
The main difference is absence of direct dependencies on any php or web-server packages. Thus, the user can (and must) provide these dependencies on their own. In other words, installing zabbix-frontend-php-deprecated package on its own will not give you a working frontend. A web server as well as PHP 7.2 with its modules have to be installed manually (use PPAs / build PHP from source). We don't endorse any particular method.