The Season 12 finale is a very odd one indeed. Knots thrived on slow builds where story arcs climax during season finales. The writers, in crafting Season 12, created stories where most of them essentially concluded (and 'concluded' is generous for these particular stories) 4 episodes before the end of the season, just in time for their 300th episode celebration (which in my opinion, was a very limp offering). Then, to conclude the season, the writers spend the one episode before the season finale, mainly introducing the Brian Johnston arc, before heightening the drama for the double-length season finale, including out-of-nowhere plots like Jason being involved in gangs.
My theory is as to why the writers did not continue with the rushed stories introduced in the finale, is that I can't imagine in any world Jacobs and Filerman even knew what these stories really were going, as I highly doubt there was a endgame when they were hurriedly introduced. Likely, Jacobs allowed the incoming writers to craft the stories they felt comfortable with, in the new 'darker and shorter story' style, while obviously not completely ignoring the lingering finale elements. In my opinion what they achieved with the strands from Season 12 was just about successful. Claudia's son was killed (I wouldn't have known what to do with him either), which finally blew up Claudia and Kate's relationship as it had been threatening to do since they were introduced. Brian Johnston's story was crafted into a nice simple arc including the murder of Linda (she had reached her potential) and the reasonably successful hostage episode 'House of Cards', eight episodes in. Even Anne and Benny's story, addressing Anne suddenly being made homeless in the finale (never truly convincing by itself) was flipped to provide shades of light in these darker times, although it does eventually outstay its welcome. These stories complimented the stories they actually wanted to tell, mainly, Tidal Energy and the introduction of Pierce.