If I hold down both shift keys and then release one of them, the key release is not detected by GDevelop, either via the Key is released condition, or when inverting the Key is pressed.
Here is the screen snip of the code I used to test and verify :
When the Left Shift is pressed the background is set to white, When the Left Shift key is released the background is set to black.
This works fine with just the key itself. If I hold down Right Shift, the Left Shift key press is detected and the screen turns white. But while holding down Right Shift and releasing Left Shift, the background colour doesn’t change to black. And releasing Right Shift after that still won’t change the background colour.