Why problems on just some of units

It's a cross-compatibility problem.  Everyone is using a different phone and sensors.  A good software is cross-compatible with all devices.  Myself I'm fighting an issue that no one else seems to have.  I have an iPhone 6, not an obscure phone.  But the main difference between me and others is that I don't carry my phone while I ride.  So when I return back home from a ride my 830 can't find/connect to the phone and upload my ride.  Everyone else already has their phone connected to the GPS when they finish their ride.

I don't ride with my phone either (iPhone XS Max) and don't have this problem. It immediately connects to the phone (or wifi, not sure) and uploads the activity even before I get inside..

Thanks.  I have my WiFi turned off on purpose.  I do remote rides sometimes and don't always have WiFi available at the finish.  If you don't mind please try a ride with the WiFi disabled.  I'm curious if my particular phone is causing my troubles.  In my case the sensor status page would say searching for phone but it never finds it unless I manually open the GC app.  With my 520 it connects to the phone automatically and uploads the ride without me having to touch the phone.

I’ll give it a try on my next ride on Sunday

The WiFi is only turned off on my 830.  The GC app. on my phone has access to WiFi and cellular data.  And I just verified that the GC has 'background app refresh' enabled and 'cellular data' enabled.