Watch asks to login during swim workouts

My watch often asks me to log in when I'm swimming. It only does it in one pool, where I think it has some WiFi signal. I also use another pool where there is no WiFi and this problem doesn't happen. All my swim workouts leave the phone too far away Bluetooth to work.

It's extremely frustrating, since I can't see anything and I can't pause the workout. Instead, I have to unlock the screen, cancel the login (I've also logged in manually, but that doesn't help for the next time), all before I can return to the workout to pause the timer.

All notifications get paused during my workouts, so I would have thought that the watch would avoid connections to iCloud during a swim. I should probably go into airplane mode before swimming, but I forget, and I'll definitely forget to reconnect the watch when my swim is finished. Is there something else I can try?