You changed your control to U32. That would not be any different to setting the diagram constant as U32.
I don't know why you are jumping all over the place with representations. The native input for an index is I32, so convert your U8 to I32, do the desired math, and get it over with. 😉
Have you placed an U8 indicator next to the array subset in the original problem code to see what the index actually gets?