I've got used iPad mini 2 in good condition, fully erased.
After setting up the device, youtube had minimized into small window on clicking home button, which I could move.
It worked for me for 2-3 hours, now it does not. iOS is 12.1.1 and I did not updated it, I hadn't changed any settings which could potentially affect that feature, also I hadn't done any mindless clicking.
What could I do to solve this problem? I am considering returning this iPad now