Double emails

Greetings,

I’ve found this plugin quite unique and i like the logic, i do have however 1 issue i cannot resolve, which is, subscribers are always getting two email notification instead of 1 and i cannot figure out why. I tried recreating the notification, reinstalling the plugin, without success.

I tried it with user groups or only 1 email address, no difference. Only the main Admin who’s email is entered in the WP settings gets 1 email notification, everyone else gets two copies. How can i debug this? Can you help me out?