Support for the Apple Watch in Zwift is not reliable and as of August they said they were not currently working on it. They left the integration there because some people still use it, but it is not good and is a common source of frustration. To avoid that frustration, you would need to stop using the watch as HRM. I realize this is probably not a welcome thing to hear but that’s the situation.
After reading your comment I was also a little confused about whether you understand that the Companion connection to the game depends only on WiFi. Devices being bridged to the game via Companion would use Bluetooth to reach the Companion app, and WiFi to be bridged from Companion to the game.
It sounds like a Wi-Fi endpoint negotiation issue, possibly. If you’re running Zwift on a Mac and haven’t used it for a while, have you tried to toggle the network permissions on the Mac side? If that option isn’t available, you can reinstall Zwift and it should come back. There can be inconsistent connection behaviour between iOS and Mac devices without this. If the toggle is there, try to toggle it off and on to see if it sets the correct permissions to hold the network connection while the process is backgrounded.
