I feel you! I had an ASP.NET Core Web API using a SQLite file for data storage. It was working exceptionally fine in development. When we released it, as soon as more than 10 users were throwing request upon it, it got so deadly slow. Obviously caching and some tweaking helped a lot. But it was far from easy to find, understand and test (!) all required options and optimizations.

Other than that I still love SQLite.