They probably made two different films with all the reshoots they did.
Well, if you look at Kylo’s death closely, it seems to have been shot in reverse AND he says something before he lays down/gets up.
I suspect Kylo lived in at least one or two shoots.
That was debunked long ago. Scenes of people collapsing like that are often filmed backwards to prevent the actor being injured. The whole “Ben lives in an alternate ending” conspiracy theory was just made up by desperate Reylos after the movie’s release.