Ok .. APM changes things.
There are a lot or redirects that take place, and the standard HTTP_REQUEST events are not always going to fire as expected as there is some "hidden stuff" happening on the VIP that you don't get exposure to.
See HIDDEN EVENTS at
https://devcentral.f5.com/articles/http-event-order-access-policy-manager.UzNOCc_NvX4
Hidden Events
For APM internal URIs, like /my.policy and /my.logout, the HTTP_REQUEST/HTTP_RESPONSE events don’t fire as you would expect beginning in v11.x. ..... However, with APM, if you require access in your iRules to these internal URIs, you can use the ACCESS::restrict_irule_events command in the CLIENT_ACCEPTED event to expose them. An example:
Hidden Events
when CLIENT_ACCEPTED {
ACCESS::restrict_irule_events disable
}
when HTTP_REQUEST {
if { [HTTP::uri] ends_with "/my.logout.php3?errorcode=19" }{
HTTP::redirect "/"
}
}
You need a full HTTP Watch trace to see what is going on