Problems with Login and sync

Coming from Wunderlist, To Do has been a nightmare since the migration.

- After a day, I have to log in again, but it fails. I have to delete the app from IOS, and reinstall to make it work again. Every day! Even a ticket raised to MS did not solve my problem.

- Since today I now have synchronisation issues. Even the web instance fails to sync. New tasks in the MacOS installation appear nowhere else.

Any input or idea would be greatly appreciated!

Tom