Mobile App network problem

Hi there! I just started using AstroPrint. I don’t even have an assembled 3D printer at the moment but I already started to test AstroPrint on my Raspberry Pi 3.
There are 2 problems. I connect the Pi to my Wifi network and my phone to the same one. The app shows “local access” and everything works fine. After a few seconds the controls stop working because it shows me that “I have to be in the same network”. And the “local access” disappears.
I am always in the same network and everything works fine in my browser. After a few seconds/minutes it starts to synchronize and everything is find again.

Same problems with my Logitech webcam. Sometimes the video stream is fine, but it always gets interrupted by an error.

I have a very stable network at hone so I don’t know what’s going on there.