Impossible ssave the old world

Hi I open my old world and convert it correctly with the new update and I can play well without problems but every time I close the game correctly, I cannot open the world anymore!  I tried to uninstall the game, reset the play station but this problem persists.  After saving and closing the session if I create a copy of the world and try to open it the game crashes.  I've noticed that it takes a long time to load resource packs and when it does it doesn't open the world.  What can I do?