2 usb serial converters on Mac stop working require reboot to fix


I have two USB to serial converters attached to Mac laptop, dell USB docking station. Mac is running Sierra. Using 2 CoolTerm windows, things work for a while, but at some point when I disconnect I get the spinning beach ball on at least one CoolTerm, have to force quit, then the devices will not work properly again (at least not both of them) until I reboot the Mac. Looking at tool uhubctl, only one is detected, sometimes I see two on the same port (4 here) and port 2 is where the other one is plugged in. As you can see, the driver is not loading there in this case (see below). Also switching ports, powering them down and up via uhubctl does not fix it…

Current status for hub 20-1.3 [0451:8044 BD020849AF6E, USB 2.10, 4 ports]
Port 1: 0503 power highspeed enable connect [0424:2137 SMSC USB2137B, USB 2.10, 7 ports]
Port 2: 0103 power enable connect ]
Port 3: 0503 power highspeed enable connect [0bda:0307 Realtek USB3.0 Card Reader 611190018901]
Port 4: 0103 power enable connect [067b:2303 Prolific Technology Inc. USB-Serial Controller D]