Apple Watch Ultra 2 needs a safe reset or will not reset

The checks in more detail

the Watch app, My Watch, All Watches, the Info button next to the watch, Unpair Apple Watch; a cellular Ultra asks whether to keep or remove the plan. Apple's page on unpairing notes that the iPhone makes a backup of the watch first, so you can restore it. If the iPhone is not available, erase from the watch in Settings, General, Reset, Erase All Content and Settings. The Ultra 2 supports Backtrack and Dive data that sit in the backup. Keep the watch on its charger during an erase.

If your Ultra 2 is cellular and you erase it, remember that the cellular plan stays with the carrier, and you re-add the watch to the plan when you pair it again; check with the carrier for any fees. If you are passing the watch on, remove the plan as part of unpairing so that your number is not left on the device. These details matter more on an expensive watch. Many owners reset an Ultra 2 before selling or after problems with custom Action button settings and Workout views; remember that Workout views, Action button assignment and custom watch faces are restored from the backup, so a clean set-up avoids bringing back a faulty setting.

If the Ultra's behavior is odd after restoring, set it up as new and rebuild your settings one at a time, noting which change brings the problem back. If your Ultra 2 has a custom Workout view or an Action button setting that you rely on, take a screenshot of each setting before you erase, so you can rebuild them. The watch's backup keeps them, but a clean set-up is a good way to test whether a setting caused your problem. Compare the behavior before and after to decide which approach to keep.