I-rule between VIPs on two different physical F5's

I would guess that the SSL disable is happening too late.

I would try the third example is this post https://devcentral.f5.com/wiki/iRules.ssl__disable.ashx

From the post .... Note: Disabling SSL on the serverside only applies before serverside connection has been established (SERVER_CONNECTED) or when the clientside of the connection is in a detached state (e.g., oneconnect, LB::detach).