I made the mistake of choosing to upgrade the Reminders database when I installed iOS 13. This broke syncing on GoodTask and another iOS reminders app I use, 2Do. In the course of trying to figure out a solution, I deleted my main iCloud list on GoodTask.
Then I realized I could fix the syncing and revert to the old database by restoring that list via a 2Do backup. (Maybe the same thing is possible on GoodTask?) Now my reminders are syncing again to my Mac's GoodTask app ... but I can't figure out how to get back the list I deleted on my iOS GoodTask. (I created a new list with the same name as the old, but it won't sync.)
Any advice welcome ...