I think the causality rate indicates how much his respawn is left. If it reaches 100%, he probably can't respawn anymore. And if that happens and he needs to turn back time, he will have to start again from the beginning, thus the system that says "Loop : 1"
Either that, or Causality rate is just how close their world is to be destroyed. And when it gets so bad, he needs to loop again to the beginning
To me this feels like a timeskip or a alternate timeline. I lean on the alternate timeline side more because a timeskip just doesn't make sense and doesn't feel right imo.
did we skip some arcs lmao, i guess this is one of the bad endings to show how the world would be, a if he survived the first day of the resurrection. This is 7 years after the first day of the school btw, assuming that the demon king is summoned after 3y this is the fourth year after the resurrection