Hi there,
errors like these are logged in your error log. If you can’t find it then contact your host and they should be able to assist.
You can also enable wp_debug and wp_debug_log:
https://codex.wordpress.org/Debugging_in_WordPress
Any errors that get logged may appear in wp-content/debug.
Other steps to try is to ensure that your server is running the latest version of PHP should at least be 7.x and that there is sufficient PHP memory 128meg upwards.
Also try disabling all plugins to see if the issue resolves and then re-activate one by one to see which is causing the issue.