Hello,
This message is a solution, not a problem 
I migrated 2 moodle platforms from MoodleCloud.com to a dedicated server.
After the migration and for these 2 platforms, I had problems with H5P activities.
Impossible to create a new H5P activity and impossible to use an existing H5P activity.
Same problem on both plateform.
The problem seems to be that some H5P libraries are missing.
And the parameter slasharguments was not activate in the config.
1/
- Manually delete all H5P content types and libraries via the URL mymoodleurl.com/h5p/libraries.php
- Force execution of the task \core\task\h5p_get_content_types_task.
This can be done by changing the task schedule or in CLI (php admin/cli/scheduled_task.php --execute='\core\task\h5p_get_content_types_task').
just forcing the scheduled task wasn't enough, I was forced to delete them first.
2/
In moodlecloud hosting, the 'slasharguments' parameter is configured in config.php.
When the config is exported, the moodle configuration store in the sql dump does not have the 'slasharguments' option enabled.
And make sure your web server config is "slasharguments compliant" : https://docs.moodle.org/403/en/Using_slash_arguments
Voila.
I spent som hours to solve these problem.
And the problem was identical on 2 differents moodle from the hoster moodlecloud so i supose that other moodlers can have the problem.
If this message can be useful to someone.