iphone/ipad rapidly disconnect and reconnect from router

I have 2 different routers but they are essentially the same router. An Asus RT-AC68U and a Tenda AC1900(AC15). My laptop and desktop will connect to these routers with no issue. Any iOS device that tries to connect will look like it's going to connect for about 1.5 seconds and then disconnect for about a second and then reconnect for a second. It will do this forever until I turn off the wifi or Forget the network. I have reset network setting on the ios device. I have updated the Firmware on the router. I downgraded the firmware on the routers. I've tried various setting within the iphone and the routers but nothing has helped. Google searches show people with connection issues but nothing that sounded like what I'm dealing with. A lot of posts say to just get a new router but one of these routers was working for a long time up until 2 days ago. I reset the router to repurpose it and this is what I have run into.