Same problem here with pro version:
AH01071: Got error 'PHP message: PHP Warning: count(): Parameter must be an array or an object that implements Countable in /var/www/vhosts/ktmdeutsch.es/httpdocs/wp-content/plugins/sticky-side-buttons/ssb-main.php on line 217', referer: https://xxxxxx.es/wp-admin/
Plugin installed successfull, the problem is in the activation in Network. Crash directly.
If I change the multisite in "false" and installed the plugin, in the reactivation of network "critical problem" and i need uninstall the plugin again