For anyone still getting this errors every now and then, ensure to check the following:
-Right-click root folder of your project and select “Update Redirector References”
-Check that you don’t have random objects in the scene under the landscape
-Check your Group actors, sometimes ungrouping all of them will fix the error
-Check all devices and verse for any references under “events” or “functions” for objects or devices already deleted
Thank you for all the help, I just wanted to share what it worked for me multiple times.