Unexpected Apple ID password prompt - Which App is causing this? I am getting unexpected prompts for my Apple ID on my iPhone SE at random times, including on the lock screen. Here are a couple of examples:

On the lock screen



In the EMail app



These started appearing a couple of weeks ago.  The prompt dialogs have no identifying information to tell me who's asking, so I'm not about to enter my Apple password until I know who's asking and why.

I have correlated these to having one specific app either running or configured for background refresh.  If the app is closed and background refresh is disabled, I do not seem to get the prompts.  

The app is Appigo ToDo, which has a cloud-based component that does require sign-in.  However, 


I am already signed in correctly to ToDo Cloud, and if I just dismiss the prompt (Cancel) without entering anything I get no error, and ToDo Cloud proceeds with no issues;
If I enter my password for ToDo Cloud, the error message is 




So, something, possibly related to Appigo ToDo Cloud, is asking for my APPLE password.  

Question(s): Given a password prompt dialog, is there any way to determine the source of the request, and the reason for the request?  What else could be causing iOS to be prompting for my Apple password at random times?
Perhaps this snippet from this help page at Appigo will provide a clue:


  iCloud is different from the other synchronization services supported by Todo in that Todo does not actively control when synchronization takes place. When you make changes to your tasks Todo flags its data as having changed; iCloud watches for this flag and synchronizes as needed. In short, while Todo can inform iCloud that it needs to be synchronized, it cannot start or control an active synchronization.


I think that ToDo needs you to manually login to iCloud, which uses your Apple ID for authentication, to sync because the saved password is incorrect. Perhaps you need to reconfirm the login credentials within the ToDo app so it syncs correctly.