Installation and server related problems

As soon as I click on anything on top of the Homepage (Examples & downloads, Documentation, Goals & roadmap etc) I keep getting logged out for no reason. As soon as Im clicking on Log in im logged in again and so on. Thus when I try to answer any comment it keeps on saying "Log in or register to post comments". When I click the Log in the homepage only gets refreshed and Im not logged in no matter how many times Im trying to log in. The only way to log in is to click the button on top of the homepage but after clicking anything else Im logged out immediately.

I am not using drupal, moodle or wordpress.

I am using another LMS.

The  php.ini has all settings ok.

But when I try update or install the content "Arithmetic Quiz" (or another), the error The file you uploaded is not a valid HTML5 Package (It does not have the .h5p file extension) comes up.

I need help.

Hi, i am usiung h5p plugin for wordpress and the actual wordpress-version 5.4.1 reports in the plugin list:
compatible until 5.3.3
this plugin is untested for your version of wordpress.

Question 1: Is is unsafe to use h5p on the current wordpress 5.4.1?

Question 2: Or do I have migrate back (all the other plugins, theme-development, ...) to the last compatible 5.3.3 Version?