[solved] An active PHP session was detected, Error in REST API

After update latest version the plugin causes the errors named in topic.
I rolled back to 7.1.7.1 – the errors are gone.

edit: folloing message I received:
Uncaught Error: Class “Microthemer\Common” not found in /…/wp-content/plugins/microthemer/src/AssetAuth.php:216
Stack trace:
#0 /…/wp-includes/class-wp-hook.php(308): Microthemer\AssetAuth->addFrontendData()
#1 /…/wp-includes/class-wp-hook.php(332): WP_Hook->apply_filters()
#2 /…/wp-includes/plugin.php(517): WP_Hook->do_action()
#3 /…/wp-admin/admin-footer.php(78): do_action()
#4 /…/wp-admin/update.php(182): require_once(‘…’)
#5 {main}
thrown