So first of all, you should literally never update a working project that is in development. Ever. It’s the worse thing you can do for both your project and your team.
Second and final, the issue is because you use an “automaterial” in the first place. Like I specified many times. Don’t use an auto material. You would never have encountered this issue.
Not sure I can make that any clearer than this TL;DR:
Engine upgrade on working project: bad practice.
“Auto” materials on landscapes: horribly bad practice.
Using landscape: horrible idea and bad practice if kept in final build.