Well, it is a start. π Are you by chance using an iPhone 12? I have seen several other people have this issue with an iPhone 12, as far as I know they never resolved the issue. I have wondered if having Location Services set to use WiFi, or any kind of backup default to WiFi if that is the issue. It can be difficult to get people to dig deeper as no one really wants to hose up their settings. I always recommend folks backup to the iCloud before doing anything.
It is a definite PITA needing to disable Cellular to make the app work. I honestly do not think it is an issue with the app, but more of an issue with the cell phone. I have no trouble with the app on an iPhone 15+ and iOS 17, an iPad Pro M4 on iPadOS 17, or an iPhone 7+ on iOS 15. I expect there are issues with other apps and their settings on some phones that users overlook.
Did you test this outside of your car using a power bank? Sometimes the cars BT or WiFi will cause issues.