sFlow doesn't export flowSampleType http

Greetings,

I have F5 BIG-IP LTM version 14.0.1 (Build 0.0.14). What I'm trying to do is to export my SLB VIP related statistics. It's referenced here in "sFlow HTTP Request sampling data types" paragraph. I configure basic sFlow collector settings in F5 GUI, run sflowtool and receive COUNTERSAMPLEs and FLOWSAMPLEs, but not with type of http. On HTTP Profile that is assigned to my SLB VIPs I have the following settings:

ltm profile http http-x-forward {
   accept-xff disabled
   app-service none
   basic-auth-realm none
   defaults-from http
   encrypt-cookies none
   enforcement {
       known-methods { CONNECT DELETE GET HEAD LOCK OPTIONS POST PROPFIND PUT TRACE UNLOCK }
       max-header-count 64
       max-header-size 32768
       max-requests 0
       pipeline allow
       truncated-redirects disabled
       unknown-method allow
   }
   fallback-host none
   fallback-status-codes none
   header-erase none
   header-insert none
   hsts {
       include-subdomains enabled
       maximum-age 16070400
       mode enabled
       preload disabled
   }
   insert-xforwarded-for enabled
   lws-separator none
   lws-width 80
   oneconnect-transformations enabled
   proxy-type reverse
   redirect-rewrite none
   request-chunking preserve
   response-chunking selective
   response-headers-permitted none
   server-agent-name BigIP
   sflow {
       poll-interval 0
       poll-interval-global yes
       sampling-rate 0
       sampling-rate-global yes
   }
   via-request preserve
   via-response preserve
   xff-alternative-names none
}

I need to gather HTTP related statistics from my TLS-enabled VIPs, but I don't receive proper sFlow samples from F5. What could be the problem?

Thank you.

• Dima