the correct one is
+ActiveClassRedirects=(OldClassName=”MyClass”,NewClassName=”/Script/Project.MyNewClass”)
it should have worked… try again maybe ? 
was the class defined in a pluggin ?
try with ‘/Script/Project/’ for the oldclassName aswell, but it worked without it on my project
if you keep the old class, does the type of the variable in blueprint still good or already as a UObject ? ( maybe the problem is somewhere else )