This worked for me when both of my updated Iphone 6’s would not connect to the home network due to a failed password. Other devices connecting fine with my known password. I went in to the wireless router and changed the bandwidth of the 5g from 40 to 80Mhz. BAM! All is working just fine. I had read on a forum change from 20 to 40 or 80, I was already 40 so went to 80. Hope this works for you, I spent hours incredibly frustrated by this.