iRule not hitting default pool?

it could be because you are searching on http::path, but im not 100% about this. But i have made a suggestion, that takes a slightly different approach:

            when HTTP_REQUEST {
              if { [string tolower [HTTP::uri]] starts_with "diagnostics"} {
                pool pool_group2
                persist source_adr 255.255.255.255 1800 
                  }
             else { pool pool_group1 
              }
            }