Summary While parallel testing Core Location on the new iOS 26.1 beta (23B5044i), I observed what I believe to be a regression of the issue described here: https://developer.apple.com/forums/thread/779192 Specifically, user positioning underground subway stations is noticeably inaccurate on the beta, whereas the same scenarios remain accurate on the unupgraded device below. I work with the MTA (New York City) and work with the OP of that thread. Happy to provide additional testing or details if helpful. Please let me know what else you need. Test Info Riding NYCT from Wall St to 34th St Penn Station on the 2 train carrying two iphones Recording: https://limewire.com/d/dpTWi#pDC3GRYIdE Expected: Consistent underground positioning comparable to prior releases. Actual: Degraded/inaccurate underground positioning on iOS 26.1 beta. Test Devices Left Screen: iPhone 15 Pro Max - iOS 26.1 beta (23B5044i) Right Screen: iPhone 11 - iOS 18.6.2 (22G100) Blue dots show location set by CoreLocation. Red dot on iphone 11 shows the actual location of both devices as I was able to manually place while travelling through a station. Placement through tunnels is not easy to verify and not usually indicated. Timestamps Comparison of when train was actually observed in a station vs when 26.1 and 18.6.2 CoreLocation updated to the station Fulton St 1:48 iOS 26.1 correctly updates (correctly) 2:16 iOS 18.6.2 updates (28sec late) Park Place 4:12 train arrives 4:15 iOS 18.6.2 updates to ~near Park Place 5:04 iOS 18.6.2 updates to Park Place (correctly) 6:07 iOS 26.1 update to ~near Park Place (over 2 mins late) Chambers St 6:02 train arrives / iOS 18.6.2 updates (correctly) 6:14 iOS 26.1 updates to ~near Chambers 6:18 iOS 26.1 update to Chambers (correctly) Franklin St 6:52 train arrives 6:55 iOS 18.6.2 updates (correctly) x:xx iOS 26.1 does not update Canal St: 7:16 train arrives 7:18 iOS 18.6.2 updates (correctly) x:xx iOS 26.1 does not update Houston St 7:54 train arrives 8:00 iOS 18.6.2 updates (correctly) x:xx iOS 26.1 does not update Christopher St 8:37 iOS 26.1 presumably between Houston St and Christopher St 8:40 train arrives / iOS 18.6.2 updates (correctly) x:xx iOS 26.1 does not update 14 St 9:22 train arrives 9:28 iOS 18.6.2 updates (correctly) 11:01 as train departs station iOS 26.1 updates (1.5 mins late)