I am using GoodTask on Mac (macOS 11.4), iOS (14.6), iPadOS (14.4).
When changing tasks (= reminders) on my iPhone and/oder iPad (e.g., check "completed"), these changes are not synced to my Mac.
I have to de-select reminders from the iCloud elements on my Mac in System Preferences and then reselect them. Then the changes are being updated to the Mac.
I can see this behavior since a few versions of GoodTask.