App sync confusion

At work we use an app for documentation and form completion. The app is installed on Lenovo tablets and will open up when users log in. The problem is that I can log in to the app and it will sync usually within 30-50 seconds. Once I log out another user will then log in, in the same location on the same tablet but it doesn’t sync beyond 20%. We’ve been on to the app development team’s support and our external IT support and neither of them have found a solution. What could be the issue?