random endless loading and error message

Does it happen even when NinjaFirewall is disabled?
It looks to me that you’re having issues with your database (bottleneck?).
Try to put WordPress is debugging mode:
1. Edit your wp-config.php
2. Search for:
define('WP_DEBUG', false);
3. Replace with:
define('WP_DEBUG', true);
4. Add this line below:
define( 'WP_DEBUG_LOG', true );

The log (if any) will be located in “/wp-content/debug.log”.

did this and the logfile looks good. as the problem didn’t occur again it was probably hosting-related. sorry for bothering you.

@nintechnet ok so after this happened again for a few times, i made contact with my provider. they referred to this article and said, sth like the firwall opens a connection for every plugin etc and it can occur that there’s too many connections. which apparently they can’t change. basically they recommended to switch to another firewall plugin. i’m a bit lost tbh

I really don’t know what they mean about “opens a connection for every plugin”.

Enable debugging in WordPress:
1. Edit your wp-config.php
2. Search for:
define('WP_DEBUG', false);
3. Replace with:
define('WP_DEBUG', true);
4. Add this line below:
define( 'WP_DEBUG_LOG', true );

The log (if any) will be located in “/wp-content/debug.log”.
It may display the reason why you’re having issues.

After debugging, undo the above modifications.

i did that. the log contains an undefined variable and 2 google maps scripts are called in an incorrect way. those things keep appearing in the log all the time.
when the problem i described happens, nothing else is logged

Could you ask your host to give more detail about the issue, i.e. about their “opens a connection for every plugin” response?