I don't know if it's a coincidence, but this only started happening when I changed residence recently and started using fiber internet.
This only happens with HBO Max and Disney+, Netflix and Prime Video work fine. I'll be watching a serie or movie for a few minutes and suddenly "HBO Max and encountered a problem". I'll go to the Mibox home screen and the wifi is turned off. I turn it on and after a few minutes it happens again.
I called my ISP and they changed the modem channel and bandwith, but it didn't help at at all and it doesn't happen on my smartphone so I guess the problem is in the mibox itself?
I don't even know what to google to solve this, I have no idea what could be.
if all else fail, you could always try factory resetting the device. Or get a usb to ethernet adapter (iirc the mibox has a usb port, but no ethernet port). Or maybe it has something to do with the app's permissions? You could try checking those out as well