Hello,

Scan again with higher accuracy (Settings -> Options ->  Performance and choose High-accuracy scanning and move slider to the  left.

The same issue at me. High accuracy and slider on the left - scannig is looong and no MAC is shown....  

Most likely, you cannot scan your computer due to the fact that it is on a different network, or the computer you are scanning has a ban on scanning (antivirus and or firewall)

Manufacturer identification is linked to the vendor portion of the MAC address which is typically the first 3 sections.  i.e. a MAC address of ab:cd:ef:12:34:56 would use ab:cd:ef to identify the vendor.

MAC addresses are a layer 2 address are so are not included in routed packet information which is layer 3.  When traffic traverses a router, the router strips the MAC address and replaces it with it's own and uses the ip address info to forward on the traffic to the new subnet.  When it reaches the destination subnet, the router will ARP the network looking for the destination MAC address of the IP address it's trying to contact, getting the ARP response from the switch infrastructure and forwarding on the traffic.  That is why switches ARP tables only contain MAC addresses for networks they are physically connected to.

If you want the MAC, and thus the manufacturer, displayed you'll need to be connected to the network your scanning.