IOS devices fail to connect to WiFi when pairing to cameras and light bulbs. I purchased an Android tablet and paired Instantly. This worked 6 months ago but now
I have a 6th Gen iPad an an iPhone X and both connect just fine. When I am pairing devices that need the 2.5GHz network I have to explicitly tell the phone or iPad to “Forget” the normal 5GHz connection and I have to manually connect to the 2.5GHz network.
Perhaps something similar is causing you issues?