Check Network Settings
Let's verify your network configuration for WiFi-connected scanners.
Verify Network Configuration
If you're using a WiFi connected scanner, make sure that your anti-virus software, firewall or router between your computer and scanner isn't blocking mDNS responses (UDP port 5353) or Canon responses (UDP port 8610 and 8612) from the scanner from being returned to VueScan.
Also, make sure you aren't using a Virtual Private Network (VPN) because this will interfere with finding scanners on the network.
If you're using a VPN, try temporarily disabling it to see if that resolves the scanner detection issue. You can re-enable it after scanning is complete.