Okay,
I would like to understand your first issue before looking at the category stuff. So, your receive 6 messages, this is already strange
If you use the Web Interface to send a notification and do not set a variant , do you have the same result ? (Or by sending a CURL directly to the Server ? )

Sinan Yasargil Hi ! So, you have the category issue but do you have also the issue of multiple messages being received even when no category is set ?