This problem often occurs due to the following reasons:

Hardware Limitations: iPhone 15 Pro’s GPS or network-based location may sometimes fail if it cannot get a clear satellite signal (like indoors or in areas with limited cell service). This error can occur if the device briefly loses location accuracy, which may be why it happens inconsistently.

Location Services Settings: Ensure that location services are enabled for the specific browser (Safari or any other you’re using) and that the app has permissions set to "While Using the App" or "Always" in iOS settings.

High Accuracy Mode: Sometimes, setting enableHighAccuracy: true can be challenging for the device if it cannot find a GPS signal, which causes POSITION_UNAVAILABLE errors. Try toggling enableHighAccuracy to false to see if the frequency of errors decreases.

Privacy Restrictions: iOS has stricter privacy settings. Make sure that the site has permissions and doesn’t trigger any privacy-related interruptions, especially in Safari. Sometimes private browsing mode in Safari can also limit geolocation.

Potential Solutions Fallback to Lower Accuracy: If high accuracy is not critical, you could set enableHighAccuracy: false. This uses Wi-Fi and cellular networks for location, which might be more reliable indoors or in places with low GPS signal.

Retry Logic: Implement a retry mechanism that re-requests location data if POSITION_UNAVAILABLE is encountered, rather than terminating immediately. A recursive function or a setTimeout could re-call watchPosition on failure after a few seconds.

Debugging Location Services: Reset location services on the device by going to Settings > General > Reset > Reset Location & Privacy. This can sometimes fix issues where iOS location services behave unpredictably.

Alternative Approach: If precision is not the top priority, consider using getCurrentPosition periodically instead of watchPosition. getCurrentPosition generally has fewer issues with errors but would require you to re-invoke it to get periodic updates. This is picked from https://thespotifypremiumapks.com/