My personal sign is when you start seeing awkward collaborations start cropping up. One time when I was thrifting, I picked up a graphic novel that had the Justice League, team with the Power Rangers of all things. I glimpsed into what the plot was about out of morbid curiosity and it was just a plain generic time and dimension thing.
Nothing ever connected between the teams at all. DC Comics, while fledgling at times with how they go about their series and movies, still have far more relevance than Power Rangers do. I think the Power Rangers are just grasping at straws to keep being relevant when people have largely moved on from them.
I’m kind of ambiguous about the first point. I think you can expand on a tightly-written, concluded story… but not repeatedly. Furthermore, it requires you to - to some degree - shift the focus of the following stories. Continuing the meta-story is all and just fine, but the immediate story can’t be about the same theme/issue/encounter indefinitely.