Safari: Picture in Picture stopped working with no reason 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
YouTube doesn’t offer Picture in Picture unless you have a YouTube Red subscription. The fact you could do it before was possible a glitch.

How can I run a YouTube video in Picture in Picture mode on iOS? on how to do Picture in Picture for free.