F5 BIG-IP Cookie Information Disclosure Vulnerability

The cookie rewrite method should only work if the server was sending a "BIGipCookie" cookie, which I'm assuming you are not. So the likely reason the message went away is that you're not sending a persistence cookie at all. A "general database error" could be indicative of another problem, but I would create a NEW cookie insert persistence profile and give it a specific cookie name value.