First of all, thank you for taking the time to try and help!
I can't share the project sorry, and getting footage of the issue would be very cumbersome so I hope you believe me that I described it exactly how it appears.
This is how the shadows(MeshInstance with PlaneMesh) should look like:
Shadows while debuging in godot on PC
But when I publish the project or use the quick test feature for android, the shadows start out invisible for the balls at the top and slowly fade in as they come closer to the camera.
The Shadow PlaneMesh does have the Transparent flag turned on, and the material is Local To Scene if that helps.
I honestly have no idea what the problem could be. Not like I specified culling or a fade-out effect anywhere. The only thing that happens is that the mesh gets moved each frame to make it look like a shadow.
I know the distance to the camera is what makes them fade in but that's about it.