iRule not working since upgrading to 11.2

It was the $:: prefix breaking the iRule on 11.x.

Adding to Niass' suggestion, you could also add your user-agent strings in lower case to the data group and then set the User-Agent header value to lower case in the iRule:

when HTTP_REQUEST {
   if { [class match -- [string tolower [HTTP::header "User-Agent"]] equals UserAgentBlacklist ] } {
      drop
   }
}

Aaron