A question

How can delete the movies I've seen from the list Social / Recommendations?
Many thanks

A movie will automatically disappear from your Recommendations page after you mark it as Watched or, on the contrary, "Not interested".
Sometimes the page is slow to update, though.

Yes, I think it is the latter you said, it takes long time to update. Because there is no way to delete it.
Many thanks for your explanation The O.P. :)