Using the Collector app on an iOS device and when I click on the Collector icon it prompts you to use ArcGIS OnLine or Portal for ArcGIS. Normally when you click ArcGIS OnLine it prompts you to enter username and password. On this device it is blank after clicking ArcGIS OnLine.
Device appears to be working fine, can access the web using Safari, etc. Have logged in to ArcGIS organizational account using Safari, etc.
Not a hiccup. Tried that several times and finally just hit the Try it icon and entered generic ESRI site. Then click on the box with up arrow and Sign In. Then the sign in window opens and I'm able to sign in.
No idea why, but at least there appears to be a work around.