Could be the version of the OS on your device.
No, sir.
My phone is pretty ancient but it's not on the google play website at the moment either. I'll see if it's back in a few days.
I don't trust any of these app/card 'banks' including Revolut. You see people in consumer moaning columns running their lives through them suddenly getting cut off completely and when it goes wrong you have one phone line that'll never get you to a real human. They're strictly toys for very occasional, and very low value, convenience as far as I'm concerned. I'll never go further with any of them.
I think I've got £24 on Wirex and £5.50 on Revolut. That feels about right.