I’d love to use the companion app, but mine works maybe 5% of the time. I can’t tell you how much time I’ve wasted in rebooting the computer, rebooting the phone, rebooting the app, making sure I’m on the same network, rebooting the network. Why does it so rarely work?
Must be your wifi environment because mine works all the time, never any issues 
Are you keeping the companion app updated on your phone, what about the phones main software (I use a samsung android and always do the software updates) what phone and version software are you using?
What is your wifi setup? Are you using a wifi repeater where you’re Zwifting, or a multi-node mesh network?