Ok, at this point, I think the best way to approach this is to take a look at the project.
Can you invite me to your organization and share the group with me?
Sum of the offline discussion on this issue. The named user was a Dispatcher and not a Worker in the project being opened using Workforce (Android) mobile. Dispatchers do not have access to the project through the mobile app.
Once Timo added the user as a Worker to the project, the Worker was able to open the project.
We'll be improving the message displayed to the user when they attempt to open a project to which they do not have the proper permissions.
I have the same issue as Timo. I am trying to make the Workforce for ArcGIS app work on an Android phone and tablet. The workers are able to log in with their usernames and see the project. However, when they try to open the project they get the error: Couldn't open project. The users are Mobile workers and not a Dispatcher. They are also part of the group where the project is stored within the ArcGIS Online environment.
When I try the same workflow on an iPhone or iPad it works fine.
Can you please help me with this issue as all our workers work with an Android-based device...
Which Beta of Workforce on Android are you using?
Can you add my named user to the project as a worker so I can take a look? You can do this by unchecking "Only search for users in my organization." on the Users tab.
We use the Workforce for ArcGIS beta version 0.2.1 (build 1483) on an Android phone which has an Android version 6.0.1. I will add you to the project.
Thank you for your effort!