If you use a wired connection to the reader and also a separate WiFi connection to the internet then Windows ( in its self acclaimed ultimate wisdom) may try to send traffic for the Internet out on the wired connection as it assumes that wired is best.
You can try using an USB to Ethernet adaptor and have a wired connection to your router.
Don't use Automatic self assigned IP addresses on your router.
Set the reader IP address ( you are using fixed IP addresses?) to a different subnet than the WiFi router.
Remember Windows think it knows best even when it doesn't
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