My understanding is that once you are in Arena, you can't leave (web and app both enforce this). Even if you are not actively playing (e.g., waiting for your next game to be paired and started).
@Martin_Stahl, If I am wrong about this please let us know.
I guess it's a bug, not a feature. Happened to me twice in a row now:
1. I'm playing a rapid Arena on my phone, android app.
2. I search for next game in Arena. Due to my rating, it takes a while to find an opponent.
3. I switch to another app on my phone, e.g. messenger message popping up.
4. I go back to chess.com app. Instead of seeing a new game started or my search cancelled, the app is now frozen, I cannot cancel the search or start a new game.
5. I have to force-close the app. In the meantime, I see in my archive that a game was started for me, it was abandoned in 1 move, and I lost rating points.
Tl;dr - switching to another mobile app while searching for an Arena game causes an abandon loss.