My theory is that the author needed a break from the main story so they gave a somewhat decent conclusion and jumped to side stories just to be able to draw about something else. And during that time, they were able to plan out a good way to properly end the series. But since there were already 3 side stories and they technically ended the main story, they just labeled season 4 as side story 4 for a proper epilogue arc.
At least that’s what I think ╮( ̄▽ ̄)╭.

Damn we really made it here. This comic has done a full 180 and I love it. Honestly why are the side stories so much better than the main story. Did the author have a change of heart?