It’s an issue with XBox controllers. I have XBox360 controllers but it should be the same for all XInput controllers that don’t have a magic switch on the controller to force them to use Direct Input. What kind of controllers were the 4 usb controllers?
A lot of frameworks allow at least 8 Direct Input controllers and a maximum of 4 XInput controllers. If they do this they use the XInput API for the XInput controllers and Direct Input API for the rest. When doing so they filter out all XInput gamepads on the Direct Input side so they don’t get duplicates. There is no easy way to know which 4xinput controllers are accessed via XInput so they filter out all of them from the direct input enumeration. Some frameworks have a way of disabling XInput altogether in order to access all controllers via Direct Input to get past the 4 controller cap for XInput controllers. As I understand this is only a Windows issue.