I'm having problems synchronizing tasks between Apple devices. It sometimes takes a very long time for the lists on the devices to be identical again.
I am using GoodTask on my MacBook, iPhone, and iPad.
I always use the latest app and operating system versions (but I haven't updated to 16.8 on all three devices yet).
I also synchronize tasks that come from Microsoft Exchange/ToDo.
Would you open Reminders app and check if it’s syncing properly? As you know, GoodTask uses data from Reminders app and relies on its sync mechanism.
For settings, iCloud Drive is used to sync the preferences data.