Casio watches iOS - closes in background and stops bluetooth sync

This is fast becoming one of the most frustrating things. I've got an iPhone 17e but had the exact same behaviour on my iPhone 13 before this. I add my bluetooth G Shock to the app and then leave the app running in the background. All of the appropriate permissions are set so it should run in the background, except, it doesn't. It'll run fine for 12-24 hours but after this, nope, it'll stop sync'ing with the watch. So I have to open the app again - then it'll run for 12-24 hours, then stop.

I've uninstalled the app several times, turned the permissions off/on etc, but this happened on my 13 and now 17e so I'm thinking that the app just doesn't fully work on iOS because iOS seems to close it after it runs for X amount of time in the background.

Anyone have this same issue?