Can't read mouse motion inside SubViewports

Godot Version

4.3

Question

In the following tree structure the Viewports inside the SubViewports hold different players(this structure allows for split screen functionality).
These characters are rotated via mouse rotation or joystick and when there’s only one player(only one ShakeableUI instance) everything works alright, the mouse movement goes down the viewport and works as intended.

image
The issue manifests when there’s two players, only one of them uses mouse inputs but for some reason the inputs no longer go down the viewport. All the important nodes are set to either ‘pass’ or ‘ignore’ mouse system so I don’t think that’s the issue. The mouse mode is also set to captured.

Any idea to what might be happening?

UPDATE:
The issue seems to go away when changing the order in which the players are added, but I still want to understand what’s going on so if anyone has any idea as to what is happening I’ll appreciate the help very much.