Open PHP session, JS Achievements
Just a heads up for the developers...
I'm trying out the Joomsports Acievements plugin on a totally clean WP 5.7 install with only the 2021 theme and no other plugins installer and the health check warned me about an open PHP session which causes REST API to fail.
Changing "session_start();" to "session_write_close();" in [plugin folder]/joomsport-achievements/includes/joomsport-achievements-admin-install.php solved the problem for me.
I hope it helps someone. :)