HTTP Cookies when using SSL offloading

Did you try to change cookie version as described in HTTP::cookie irule wiki? https://devcentral.f5.com/wiki/iRules.HTTP__cookie.ashx

when HTTP_RESPONSE {
   set cookieNames [HTTP::cookie names]
   foreach aCookie $cookieNames {
      HTTP::cookie version $aCookie 1
      HTTP::cookie secure $aCookie enable
   }
}