I have been pulling my hair out on this issue for several days. The cam will connect with the WiFi but when you go back to the app the app says there is no connection and goes back to the home page.
Finally tried connecting to my 900 with my sons phone and it connected no problem (Samsung S8). Tried immediately connecting with my phone and no luck (Samsung S9). Finally figured out that if the mobile network is still active with the WiFi connected the cam will still connect to the WiFi network but it will not transfer data to the app and say WiFi not available when you go back into the app. Once I turned off the mobile network the app responded immediately.
So, in short, check the tool bar at the top of your phone. If the WiFi symbol is present along with the 4G icon the cam will connect to the wifi but it will not connect to the app.
My resolution, Turned off the mobile data.