how to prove fallback host triggered is due to 1 bad request respond from backend server?

1: vs1 has irule 1 ,then connection1 is established . then I made change to irule1 ,then connection2 is established. Due to irule change only applied to new connection connection2 ,so connection1 still use cached or old irule1 How to check whether connection1 still use old/cached irule 1??

i am not aware of it.

2:For the fallback host triggered problem,I made one test: one vip has server side ssl enabled,but pool behind it only accept plain http,everytime it can trigger a fallhost redirect.

i understand fallback is triggered because connection between bigip and server fails e.g. tcp reset.