The ipfix server totally knockout at that time, there was no flapping.
Here's why i'm questioning the intermittent behaviour of the http responses on the clientside, could this possibly have to do with a specific type of responses or maybe a present of an http header made the irule act funky?
It is worth to mention two minutes after the ipfix server went down a TCL error logged mentioning the last line "IPFIX::destination send .. " , and it appeared that minute only.
whereas in the irule statistics, the failure stats was increasing for the HTTP_RESPONSE_RELEASE event.