I'm just beginning to troubleshoot the issue, however I wanted to ask the question now in case someone has come across the same issue. I have a highly available portal environment with IWA (2 web adaptor servers, 2 portal servers, 2 host servers, 2 federated mapping servers). For a mobile solution, we have Collector on iOS and use a VPN through AirWatch to connect to the portal. Users are able to log in when the VPN connection is established and view maps that have been shared with them. However sometimes when users log in and load a map no layers pop up (picture attached). Reloading the map doesn't fix the issue nor does logging out and logging back in. Sometimes uninstalling and reinstalling the app works, but not always. Other times, users are able to log in and everything loads up.
What I have noticed is when services are shared publicly with anonymous access allowed they will always show up, however there is group specific data collection that I would like to not share with everyone on my network. Additionally, I notice when data is collected on the public service, the user tracking information is not recorded into a hosted feature layer. I find this extremely odd since a user has to enter their user name and password in order to log into portal to use collector thus obtaining a token. Why would that information not be passed? Based on that, it seems like it is a portal token issues or communication between ArcGIS Server and Portal, however I do not know where to begin to troubleshoot this. My guess is it would have something to do with which portal you log into, but again that's just a guess. I know my situation is unique with the HA setup, but has anyone come across any token issues before between Portal and a federated ArcGIS Server?
EDIT: I forgot to mention that I'm using ArcGIS Enterprise 10.5.1 and the latest version of collector on iOS 11.4.1