I mailed support earlier today and got this:
I’m sorry to hear you’re having issues with your PowerCal readings in Zwift. We’ve identified an issue with Power/HRM combos after the newest Zwift update. I’ve checked with our team and they’re working on a fix. This fix will come from our end and all you should have to do is keep your Zwift app up to date! As of right now, the only workaround available is to pair your PowerCal as a HRM and not as a Power Source on your Android. Also, you can always use one of the devices that is working for you until we get this resolved!
Yeah, I bought an iPad so it’s no longer an issue for me… but it would be nice to see the Android version fixed.