Even with Locline (halo type configuration to spread out the recirc below the wort level and above the grain bed), you need to flow at a rate that allows the draining through the grain bed and out the bottom of the mash tun. Recirculating too fast can cause the upper part of the mash tun to fill and then the wort may simply go through the sides of the bag above the actual grain bed, much like a channeling through grain can occur. It is really a matter of getting the system and process down on your setup.