this demo is only has custom block node ,and it cannot use ctrl + a to select all nodes
this demo add a paragraph before the custom block node, it can work
What appears to be happening is that everything works, but Chrome doesn’t actually display the selection—if I hit ctrl-a in your demo and inspect the DOM selection, it spans all across the ProseMirror element. But there’s no selection visible. (In Firefox everything works properly.) Maybe file an issue with Chrome?