Changing engine versions causes a large array of problems because new engine versions usually have new ways of using older systems. A lot of code changes and fixes have been made.
So you’ll have to scrub through your project and see exactly what systems were broken and individually fix each system. For instance, moving from .24 to .25, ALL lighting was broken. You had to go in and re-add and re-do all manually placed lighting. It was incredibly annoying.
But there’s a strong chance is a basic system like that that’s not working properly. You’ll have to search for whatever is broken manually.