iRule Issue - Calculate Average Page Response Time using Table Command

I don't have a way to retrieve average response time per page through iControl, so I wrote an iRule to do that. The iRule works fine on my local F5 but not on production. The iRule is attached to a particular virtual server on production with over 1,000 client connections on an average, I was only able to retrieve the average response time through iRule a few times, and then it always returns empty string, not sure why. I can't add logging on production because I have no control over deploying the iRule. Can someone please tell me if they see any issues from the following iRule?

when HTTP_REQUEST {
        use virtual server name as subtable name in Table command
        set tbl [virtual name]
        set requestTime [clock clicks -milliseconds]
        flag to track specified page extensions: aspx, ashx, asmx and svc
        set track 0
        constant threshold to check against and reset accumulated TotalResponseTime value if surpassed. this is a fault tolerance feature to prevent TotalResponseTime becoming too large, and
        to enable this iRule to be self-contained and be able to run even if "resetstats" below is never called.
        set timeThreshold 3000000

        if { ([HTTP::path] ends_with ".aspx") or ([HTTP::path] ends_with ".ashx") or ([HTTP::path] ends_with ".asmx") or ([HTTP::path] ends_with ".svc")  }{
            set track 1            
        }

        retrieve or reset all key/value pairs stored in a subtable in HTTP_RESPONSE event
        set kvPair ""
        switch [string tolower [HTTP::uri]]
        {
            "/getstats"
            {
                if { [info exists tbl] } {  
                    foreach tkey [table keys -subtable $tbl] {                                 
                        lappend kvPair "$tkey:[table lookup -notouch -subtable $tbl $tkey]"                     
                    }
                }

                HTTP::respond 200 content $kvPair               
            }  
            "/resetstats"
            {
                if { [info exists tbl] } {  
                    foreach tkey [table keys -subtable $tbl] {      
                        table set -subtable $tbl -mustexist $tkey "" indefinite indefinite
                    }                                   
                }

                HTTP::respond 200 content "success"             
            }
        }
}

when HTTP_RESPONSE {
        set current page request response time
        set curResponseTime [expr {[clock clicks -milliseconds] - $requestTime}]

        if { $track == 1 }{
            lookup current TotalResponseTime stored in subtable
            set storedTotal [table lookup -notouch -subtable $tbl "TotalResponseTime"]
            reset values stored in subtable if passed threshold
            if { $storedTotal > $timeThreshold }
            {
                table set -subtable $tbl -mustexist "TotalResponseTime" "" indefinite indefinite
                table set -subtable $tbl -mustexist "TotalRequests" "" indefinite indefinite
                table set -subtable $tbl -mustexist "AvgResponseTime" "" indefinite indefinite
            }
            increase TotalResponseTime value in subtable by curResponseTime
            set totalResponseTime [table incr -subtable $tbl "TotalResponseTime" $curResponseTime]
            increase TotalRequests counter in subtable by 1
            set totalRequests [table incr -subtable $tbl "TotalRequests"]
            calculate and set AvgResponseTime value in subtable
            table set -subtable $tbl "AvgResponseTime" [expr { $totalResponseTime / $totalRequests }] indefinite indefinite                         
        }
}