(Disclaimer: This is a known issue – see the links below – and this forum entry is not meant as a "complaint" so to speak, but the issue seems so important that developers on Windows should know about it. Hopefully the issue will be resolved soon, as it is acknowledged at least by some developers of Swift as an important issue.)
When using several async/await calls on Windows, an application on Windows crashes. The number of async calls until it crashes seems to be variable, depending on the application, but I have one application where I really can reduce some of the calls at the beginning and the application will work a bit further accordingly.
It first encountered the problem when trying swift-win32. Unfortunately, the application where I have the crash now is an important application of mine, and I value the async calls that it recently got as being essential to it, so the problem makes Swift currently kind of useless for me on Windows...
According to @compnerd, the issues is to be resolved in LLVM, and there also is an according bug entry for Swift.