This particular solution does satisfy correctness, although I can't share the source code (as the competition is ongoing). Feel free to provide your input data and I'll run it to compare with your expected result.
It is surprising to me that C# and .NET is comparatively under-represented in North America where it was born. Nothing but good experience in developing and operating software with it, both desktop apps (Win/Mac) and backend services (Linux).
FAST FIX protocol is terrible performance-wise, its format requires multiple branching at every field parsing. Even "high-performance" libraries like mFAST are slow: I recently helped a client to optimize parsing for several messages and got 8x speed improvement over mFAST (which is a big deal in HFT space).