First thing I always used to ask, and from my own personal experience, is what devices are the customers using?  Apple products?  I always immediately look at the router for TKIP/AES.  If it's TKIP/AES.  Move it to simply AES, WPA2. 


I'm thinking these are Apple products, and with the most recent updates, the devices simply won't tolerate the TKIP anymore..But I'm grasping at straws as I don't have any experience with Eero at all.