Hi @Sandor95, welcome to the Blue Robotics forum 
Can you explain what software you’re running on the Raspberry Pi and Pixhawk, and what connection configuration you’ve done in QGroundControl?
Some comments on the information in your post:
- Neither of the Onboard Computer softwares that Blue Robotics has been involved with supports the Raspberry Pi 2B
- The Pixhawk 2.4.8 is generally not recommended due to low quality components (although that shouldn’t be relevant to your connectivity issue)
- Using QGroundControl over wifi is not supported or recommended for use with ArduSub vehicles
- ArduSub is also not actively supported for user with QGroundControl on mobile devices / tablets
If you’re not using an ArduSub-based vehicle or Blue Robotics software then you likely want to be on the more general ArduPilot forum instead (or the PX4 forum if you’re not running ArduPilot software).