|You may have a bad port on switch B, or the switch itself may be going bad.|
You need to do some testing and report back your findings. Starting with neither laptop plugged in, first plug one into port 3 and test. Does the switch go haywire? If yes, unplug that laptop from 3 and plug it into 4. Does the switch go haywire? If yes, unplug that laptop and redo the two tests with the other laptop. I'm trying to ascertain if it's the switch or a laptop that's causing the issue.
If the test with the first laptop fails on both ports, but doesn't with the second laptop, then it's a fairly safe bet, the first laptop is the issue.
If the switch goes haywire when either laptop is plugged in to port 3, but not 4, then it's the port.
So run through the port/laptop tests and let me know what you find.
If you have one, or two bad ports on the switch, I'd just replace it with a new switch. They're relatively inexpensive and if it is a port (or ports) then you can't fix it anyhow.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.