To fix this issue kindly verify if the data on todo-cloud.com is current and correct, once it is kindly have the app uninstalled and reinstalled on your device and test if the issue persists.
Could you send us your diagnostic report from the device that you are having the problem with?
You can send it to me by doing the following:
-Open Todo, tap on the settings button/ Your Name
-Tap on "Information"
-Tap on "Diagnostics"
-Scroll down to the very bottom, and tap on "Email Diagnostic Report"
-Read the instructions of the popup message and tap on "Email"
-Please include the description of the problem you are having or the ticket ID of your support case
-When you are ready to email your Diagnostic Report, tap on "Send"
Are you receiving a pop-up each time you perform a sync?