How could you rule out the following watchpoints? Select each box and make a selection, then submit.
Select/bind EMM – Is the enterprise still bound?
Select OS version/device – Is the application supported by the OS / device?
Create/sync users or groups – Is the application assigned to the correct users and/or groups?
Upload apps – Is the private app published and targeting your enterprise?
Approve/assign apps – Is the user able to find and install from the Play store?
Set managed config – Is the app configured correctly?
Update apps/device – Did the developer update the app and ask for additional permissions?