This is a newer issue which has been occurring with QB POS v 19.
After the scanner is installed, you will need to fix a couple of settings in order for the scanner to communicate.
Open the computer Device Manager ( WIn key + R, type Device Manager).
Under the Device Manager, click on Ports.
Look for Silicon Labs, and note the COM port number. Right Click Silicon Labs and choose Properties.
On the Baud Rate, it will be at 9600. Select the Baud rate and choose 115200. Then click OK.
In the QB POS software, go to File, Preferences, Workstation.
On the left, select Physical Inventory Scanner. Then change the Attached to Com Port Number, to the Com Port Number you saw in the Device Manager.
This should allow the Physical Inventory Scanner to work.