to confirm if cookie is originated from F5 or other devices

if we are using ASM with LTM, we noticed there is a cookie called TSxxx, we had an irule in place for httponly and secureflag, but not sure why is it not working for the TSxxx cookie. Below is the irule, kindly advise.

when HTTP_RESPONSE { set var [HTTP::header values "Set-Cookie"] HTTP::header remove "Set-Cookie" foreach tcookie $var { HTTP::header insert "Set-Cookie" "${tcookie}; HttpOnly; Secure " } }