Hello @ibeebah
Welcome to Microsoft QnA !
I understand that each time you sing in to Office 365 APPS from mobile ( Is this also for Teams ?) you are prompted for a sign -in when you exit the App. (iOS or Android ?)
For starters:
Can you please clarify if Modern Authentication is Enabled on the Tenant ?
Did you tried with another account-user ?
Are you on a Hybrid Model ?
Can you please check the Sign-In Logs from Azure AD and attach some screenshots?
Any additional information would be very helpful as there are little to work with!
Thank you!