configuration for RADIUS CoA (ISE) & strange statistic

today night i was alerted by Cisco ISE engineer that my config for CoA doesnt seem supporting it.
config is done w/o deviations from How To: Cisco & F5 Deployment Guide: ISE Load Balancing Using BIG-IP - Cisco Community
my 1st reaction was quickly walking  through SNAT pool & associated VS statistics. difference surprised me a bit.
whilst pool has 0 statistics, associated VS doesnt (namely something ~16K)

How can it be?