Symptoms

JIRA Cloud users are unable to see ANY projects. You've checked application access and indeed, access to the system dashboard is all they can access.  You've also specifically added them to multiple roles and added those roles to the project(s) in question.

Cause

The default login-group defined in Global Permissions is not consistent with the Browse Project (Project Permission) and Project Role (Users). 

Resolution

• Take note of the default login group that's defined in Global Permissions. For this example, let's say its defined as being the jira-users group.
• Take note of the Browse Project permission for Project Role (Users)

• Now look at what's actually defined for Project Role (Users). For this example, its the users group, which is not consistent with the login-group in Global Permissions. This means that all new users added to the jira-users group won't have Browse Project permission.

• To remedy this, update the Project Roles for Users to reflect what's defined in Global Permissions. In other words, add jira-users to Project Role (Users)