datagroup value set to SSL?

I guess what's most troubling to me is the 500 error. That's coming from the application. You wouldn't get that error if SSL issues were breaking the connection. At this point I would probably do a Fiddler capture with SSL tunneling enabled, and then again with SSL bridging and compare the two. You can also do an SSLDUMP on either side of the proxy:

ssldump -AdNn -i 0.0 port 443 and host [VIP address for client side traffic and server IP for server side traffic] 

This will show you the cleartext portion of the SSL handshakes and if there are any errors, that's where they'd be. Also do this capture for a tunneled connection in case there's some issue with the bridged server SSL handshake that's causing the problem. Look at the ciphers negotiated and any TLS extensions that are in one but not the other. Believe it or not I've seen applications choke because there was no Server Name Indication (SNI) value coming from the server side SSL.