I do not know the used tech.
Just disable the plugins and use another FREE theme.
START
Enable on plugin and
check if problem exists
If problem exists speak with vendor
if not exists go to START
at the end enable the Theme
The Bad guy who creates the problem must not used.
Maybe to had updated the core WordPress.
Do you have an old good backup ?
The core WP does not generate logs, it is a good idea to check the Web Server’s logs.
Maybe to be an OS (linux) error, see your system logs.
What did you change and then appeared the problem ?
I hope to help.