VisibleDefaultsOnly is EditDefaultsOnly are specifiers which set access property in property editor, you can’t use both of them is same time, you need to pick one of them.
- Visible* = Read-only
- Edit* = Read-Write
In other words you trying to make your property Read-Only and Read-Write in same time
Considering you trying to use “EditDefaultsOnly” means you just need this one, so remove “VisibleDefaultsOnly”