Debugging concurrency issues isn't a syntactic process so they have to resort to println debugging. This works but isn't exhaustive and burns a lot of tokens.
replyThey do a fantastic job just by inspecting the source. It's obviously not exhaustive, but it's quite good.
replyTest it on your last concurrency bug. Point fable at the rough symptoms and ask to find where the issue is by inspection. It'll probably do just fine.