"Background" downloads disconnect game on Android

When playing Hearthstone, on Android, on a Wifi connection, about 3 minutes after starting the first game of the session, a background download always starts.

The download then kicks my phone off the WiFi (which is stable for other devices on the network at the same time) and then sits there “initialising”. If I leave it, after about a minute it decides that the download is complete, and after that I can play, although obviously I lose the game I was on when the download started. Alternatively, I can turn WiFi off on the device, and play on 4g, which then works fine. Or I can keep desparately trying to reconnect, hoping I won’t miss the turn timer.

This has been going on for ages; I hadn’t reported it because I assumed someone else would, but it has been a constant problem across the last few expansions and devices. I’m currently using a Nokia 7.2.

Anyone else get this? Anything I can do? Reinstalling the game is not the answer because swapping to a whole new phone didn’t fix it! I looked for a “turn off background downloads even on WiFi” setting which I’m sure used to exist, but I can’t find one any more.

TLDR: “background” downloads start in the middle of a game, and kick me off the network, ruining the play experience.