I'm having trouble finding a context in which a listbox would support these
values in RowSource and RowSourceType, so I can't generate a test sheet.
However, I suspect that you don't want to keep resetting these two
properties.

What happens if you set them once, outside the loop, then only do the
AddItem inside the loop?

If that doesn't give any joy, you might like to upload the spreadsheet to
the files section and we'll have a look at it.