Not the OP but my impression with asyncio was that it's great for the uses case it was built for (hence the "no problems") but if you need to do something a bit different it can become an annoyance (hence the "unexpected bugs").

I see it for a specialized solution for a specific class of problems, which can lead to surprises if your problem evolves. There are always trade-offs to be made (performance, flexibility, hardware cost, etc.), asyncio just has different characteristics than the alternatives. Maybe since a upper bound of concurrent users it is always a great (the best?) solution, someone with more experience along all the design and requirements space could comment.