Thanks for using GoodTask.
On iOS 13, there are some performance issues when you have more than several hundred tasks including completed ones. This gets better on iOS 13.1 but it's still worse than iOS 12 which worked well with thousands.
(Edited : Performance seems to have improved on iOS 13.1.2. It may need some indexing time.)
I'm preparing some updates to improve this but meanwhile you can do the followings to make it work better.
- You can remove completed tasks.
- Go into 'Settings - Advanced' and delete completed tasks. You can delete them all or delete with date options.
- Go into 'Settings - Lists & Calendars' and you can delete completed tasks per list.
- If you prefer to keep all completed tasks, you can uncheck lists that's large and make new ones.
- Go into 'Settings - Lists & Calendars' and uncheck the lists.
With few hundred tasks, it should work pretty well. I'll do my best to bring more updates soon.