I always configure the url when using arrowpoint-cookies because this feature is an L5 feature. The CSS needs to spoof the connection between client and server.
However, if it was mandatory, nothing would work as it is. Not just a few connection failures.
Your problem is most probably due to idle timeout. If the CSS detected the connection was idle, it will stop looking for new cookies in the connection, so no remapping is possible.
Use the flow-timeout-multiplier command to increase the idle timeout ie: by 25 and see if that improves the situation.
Gilles.