There is a bug with UDP signatures having detection loss in certain unique cases like VPNGate. It is currently being analyzed and fixed by the engine team. We will update you when a patch is available. An alternative would be to try the custom signatures for UDP connections. There could be some false positive risks though.
Second Please create 2 IPS signature for UDP connection Below:
/ip firewall address-list
add address=220.127.116.11/24 list=LAN
/ip firewall layer7-protocol
add name=opera regexp="^.+(opera-mini.net).*\$"
/ip firewall filter
add action=drop chain=forward layer7-protocol=opera src-address-list=LAN
Basically it will block anything going to opera-mini.net
How to achieve that in Fortigate
FYI I am using Fortigate 5.4 Unlicensed in Unetlab
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