Need some help in understanding stick table rate limit

We are using haproxy v 2.2

i have an frontend which handles few incoming APIS so i would like to control the limit in haproxy so that i can control my outgoing requests to outbound.

frontend http

bind tfo accept-proxy
acl is_ssl fc_rcvd_proxy
option nolinger
stick-table type binary len 8 size 100k expire 10s store http_req_rate(1s)
http-request track-sc0 path
http-request set-var(req.rate_limit) path,map_regm(/usr/,500)
http-request set-var(req.request_rate) path,table_http_req_rate()
acl rate_abuse var(req.rate_limit),sub(req.request_rate) lt 0
acl is_rem path_reg /ann/user/[^/]+/remoteDestinations
http-request deny deny_status 503 if is_rem rate_abuse
use_backend slowBackHttp if rate_abuse

default_backend usemultipleports.

below is my contents of file
/ann/private/users 1
/ann/version 100
/ann/servers 100
/ann/user/[^/]+/remoteDestinations 3
/ann/private/options/userPolicy 80
/ann/private/user 80
/ann/user 30
/ann/clusterUser 10

i could see all my /ann/user/23/remoteDestinations API calls returned with 503 when i trigger this along with other api’s like /ann/clusterUser , /ann/user, /ann/private/user ,/ann/servers.

Any pointers here on what could be going wrong ?