No surprises here.
It always struggles on non-web projects or on software where it really matters that correctness is first and foremost above everything, such as the dotnet runtime.
Either way, a complete disastrous start and what a mess that Copilot has caused.
I have so far only found LlMs useful as a way of researching, an alternative to web search, and doing very basic rote tasks like implementing unit tests or doing a first pass explanation of some code. Tried actually writing code and it’s not usable.