Ben, you're still in Commander mode. The camera is still reporting 'return light not detected'. If you're not commanding other speedlights, get out of Commander mode. I suspect that the lack of response from the commanded units is throwing the flash system off, which in turn is upsetting the Auto ISO system. Don't know, not hugely interested, but I'm confident that if you get out of commander mode, or give the speedlight something to command, you'll get the expected results.