I had a similar question and it looks like the common understanding is that if the next crossing is not to far away the remaining part should remain motorway/motorway_link.
For 1) I would contact the administration for the highway, is this maybe some old set of signs that should been removed when the highway was extended?
For the tunnel, based on mapillary it looks to me the eastbound tube did not have the signs “ever” and for the westbound tunnel the signs are removed somewhere around 2020