There are lots of places where no more details are available. Yet the debugger shows you an expandable icon which when expanded results in "Children could not be evaluated".
ser = serial.Serial(0)
Set a breakpoint on the ser = seriall... line.
Hover over "serial"
Expand down into serial->ctypes->c_functype_cache
Notice we reach a deadend where we show we can't evaluate children
Instead of this behavior we should be more aggressive in understanding what we are looking at. If we know there is never going to be anything else to expand then let VS know that.