Since upgrading ArcGIS Enterprise to 10.6.1 we are not able to sign in to Collector on iOS. We use a VPN to connect to our network and use Portal level authentication. It looks like Collector tries to log in through an in-app Safari browser and our organization doesn't allow access to any sites using Safari and VPN. This is really puzzling to me because 1) we can connect through ArcGIS Explorer, Collector Classic and Survey123 and 2) we can connect to Collector through ArcGIS Enterprise 10.5.1.
Has anyone else experienced this issue? Does anyone have any ideas on how to fix this? Esri does not provide support for VPN configurations.