I am still having the problem, that an edit (changes like another due date) to a task reverts every time back to state it was before. I have to do every change a 2nd time, until it stays the way I had edited it.
Restart of GoodTask or the MacBook does not help.
The problem exists regardless of whether Apple Reminder is running in the background or not
In Reminders, changes work right away.
Deleting the local cache did not help.
Restarting GoodTask sometimes stops the problem, but just for a while and not not always.
Same with resetting the calender settings.
Hiding completed tasks helped, but just for a while.