Scanning multiple IP ranges

Hi,
I have 3 network ranges to scan:
192.168.5.0/32
192.168.111.0/32
192.168.113.0/32
(192.168.111.0/32 and 192.168.113.0/32 are VPN distant sites)

I can scan these networks only by scanning 192.168.5.1 - 192.168.113.254; it's a bit... long. I've tried to scan "192.168.5.1 - 192.168.5.254 ; 192.168.113.1 - 192.168.113.254", but this range is not allowed on WiFi Guard.

Can WiFi Guard scan many networks with non-consecutive ranges?

You have almost succeeded
Just make it comma-separated, not semicolon-separated. For example:
192.168.5.1 - 192.168.5.254, 192.168.113.1 - 192.168.113.254

I defined the following comma separated IP-ranges:
192.168.2.1 - 192.168.2.254, 192.168.3.1 - 192.168.3.254

Only the 192.168.3.1 - 192.168.3.254 range is scanned.
192.168.3.0 is the subnet of the PC where Wifi Guard is used.
I can ping the 192.168.2.0 subnet.
What is wrong here?

The short answer: WiFi Guard cannot determine MAC addresses outside the current subnet.

The long answer: The ARP protocol that WiFi Guard uses to find out the MAC address of a device does not work across subnets. In your case the 192.168.2.x network is behind the router, so there is no way to discover MAC addresses in that network. As the sole purpose of WiFi Guard is to identify devices by MAC address, it does not show any devices whose MAC address cannot be determined.

What about multiple VLANs? Is it possible to scan more than one?

Unlikely. As far as I know ARP requests cannot cross VLAN boundaries.

Do you have an advice, how to perform a scan over a different VLAN?

You would have to connect your PC to the VLAN you want to scan (my understanding is that a PC can only be connected to one VLAN at a time).