Thanks, @DanBrooks. Your follow-up offers a little more to go on.
I'll be third-in-line to say I use the iOS version much more than the macOS version, but on the rare occasion that I've fired up GoodTask on my MacBook, I've never experienced any beach-balling or lack of responsiveness. That's probably something for other users of the macOS version to weigh in on, however, and may be something to flag with @GoodTask if there's an issue.
I'm not exactly clear on what you mean by "not retaining sub-tasks", but you might be referring to what was raised here:
In my use of GoodTask, I've chosen to prefer GoodTask's formatting of sub-tasks. Among other reasons, it's relatively easy to add sub-tasks from appropriately formatted text lists, which suits my workflow. Again, YMMV, and I totally appreciate that this may not be ideal for you if you're sharing any of your Reminders lists with other people...