I just ran into this. The new PhotonNumber custom element does not produce a "change" event when you click up/down, which the containing element relies on to now when to call dispatchSettingChange with the new value.
Bug 1659302 Comment 6 Edit History
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I just ran into this. The new PhotonNumber custom element does not produce a "change" event when you click up/down, which the containing element relies on to know when to call dispatchSettingChange with the new value.