I had a fascinating encounter yesterday when the web application we were working on unexpectedly stopped responding. Initially, we suspected either database locking or an excessive number of requests.
However, the issue turned out to be a failed assertion from a third-party library (PdfSharp). To resolve it, we had to click "OK" on the web server PC, after which the web application resumed normal operation.
This incident surprised me because I typically don't use Debug.Assert to monitor my code's state. It underscores the importance of utilizing the release version of third-party libraries as a best practice.