Can you post the configuration for this virtual server and the iRule that you're using? Via CLI -
tmsh list ltm virtual (vs-name)
You are correct - server-ssl profiles re-encrypt traffic to the pool member, and client-ssl profiles terminate SSL connections from the user at the F5. If you are receiving a 404 response, it appears as if IP/TCP traffic is properly flowing to/from the server and that SSL handshakes are occurring, the server just doesn't have the URL being requested. If traffic wasn't flowing or handshakes weren't occurring, you would see timeouts or TCP resets, assuming the iRule isn't configured to respond with a 404.
Testing via curl may also help -
curl https://(vs-ip):(vs-port)/(url) -vv