I don't think anything in Dramatica specifically prohibits any throughline from embracing its Solution early, even before the halfway point. The RS also has more leeway than the other throughlines (i.e. you get to decide on your own whether the Solution is embraced or not, and whether the relationship ends "well" or not). So is it possible they've just embraced ENDING?
That said, it would be good if you could still hit all the signposts and show that the RS is not totally resolved until Signpost 4. There should at least be the feeling that there are problems or conflict, or the potential for then.
The Activity/Doing does not have to just be doing one thing. Maybe in Act 1 there is relationship conflict and interesting relationship story-stuff around social activities. Then, later in the story there is conflict about lack-of-Activity-together as the MC is off doing something without the IC (political campaign you mentioned). That still totally fits your RS throughline.
Similar with the UNENDING problem -- at first it might rear its ugly head as tedium, then later as "this stupid campaign will never end" or whatever fits your story.