In order to run efficiently, the Data Collector does not show the whole project list. It shows the projects that the user has access to and fit one of the following criteria:-
1) Is set as a Current Project for the User.
2) Has the "Active for Field Data Collection" option set to Yes. This is set as default for new projects and can be found on the right-hand side of the Edit Project form (You May need to scroll right to find it)
If you are in the field when you notice you cannot download the project details then you have two options. 1) Get anyone to set the project's "Active for Field Data Collection" field to "Yes" - this will make it available to all devices and users that have access to the project. 2) Open the Web Portal, Data Entry Module or Professional and set the Project as Current for yourself.