If you are using your phone for the Companion app I think you should start there. Try turning the phone signal off, so that your phone will only connect via WiFi. The app on the phone will ‘compete’ for a signal between WiFi and 4G/5G/whatever your phone is on, but the Companion app has to be on the same network as the device on which you are running Zwift. So, if the phone is on WiFi for a bit, and then switches to using your phone network, you will lose connection.
You might also try setting your WiFi router to use a fixed channel, instead of scanning for the ‘best’ channel’, if you have not already done so.
Personally, I use a WiFi-only iPad to run the Companion app, so I haven’t had to deal with the ‘signal fighting’, but it seems to be a common theme for folks who have issues with the Companion app staying connected.