I have had this bug for a few weeks now that every time I try to edit an existing world the game immediately crashes. It doesn’t matter if the world has addons installed or not it just happens with every existing world. I can create a new world and it will work but as soon as I once exit the world and try to edit the setting from in the world menu the game crashes. I have seen clips of this happening on other devices like a console or an iPad but I have not found any way of fixing the problem.
I hope this helped you to undersand how the bug works and I would be happy if you would fix it in a future update.
This issue is being tracked at MCPE-188077.