Do you know which CPU cores was it buggy in for a very long time? The ones that everyone uses had flawless support for more than a decade.

In either case, I don't see how that disproves the argument that support of hardware features like AVX in a runtime comparable to JVM can be done well.

(though I'm biased to say low-level features are a weak point of JVM and a strong point of .NET, you don't have to sacrifice high-level convenience in other areas to get that)