As a general update to the SBB EasyRide issue:
apparently, "Network Location" under Settings > Location > Location services is a requirement for the EasyRide feature to work. Disabling it reliably causes the "location accuracy too weak" error.
As @ThP and @Franco mentioned, the "Change location permissions" button does nothing when tapped.
There is a location based timetable in the same app, which still works without issues, even though the EasyRide part is non functional.
This reminded me that EasyRide is a service that's actually integrated to the SBB by a third party, called Fairtiq. They also have their own app, just called FAIRTIQ. I tried downloading that one and signing up for an account. After registering, it is showing exactly the same behaviour as the SBB App:
With Network location disabled, it's showing "Limited access to your location" with a link to a generic help article. With it enabled, it's stuck on "Searching for stations..."
Sadly both apps don't seem to write anything useful to the logcat logs.