Moving focus stops working upwards if hidden attribute is set to true of an element in the focus flow
To reproduce:
I have button that I hide when it is clicked
Start moving focus downwards till button is reached, click that button, click handler will execute button.hidden = true;
moving focus downwards if further elements are present below the now hidden button works
moving focus upwards from where the button was previously displayed no longer works
So setting an element to hidden in the chain, disrupts the focus flow upwards starting from that element