The behavior is odd, and I would think F5 should help you at least understand it, before you permanently change your setup, such as by using OneConnect....
Can you show the HTTP conversation between client and VIP, then VIP and server? preferably one that went wrong... specifically the HTTP version and the Connect header...
The client should say something like:
> GET / HTTP/1.1
Server:
< HTTP/1.1 301 Moved Permanently
< Connection: keep-alive
Maybe your clients request keep alive (HTTP 1.1), while your backend server is always requesting that every connection be closed?
Please ignore what I said about "Port translation" I misspoke and I am not sure I understand that option or the probably more relevant "Source Port"