Looks like:

    // TODO: (async) revisit and examine if this needs to be supported somehow
    if (pMeth->IsAsyncVariantMethod())
    {
        _ASSERTE(!"Async variants should be hidden from reflection.");
        COMPlusThrow(kNotSupportedException);
    }

We need to follow up on this and remove the TODOs as a result of either:

• confirming that what we have is correct. Perhaps add a comment why it is correct.
• fix the code and ideally add tests.

Most likely we should not see Async Thunks here and just an assert would be enough.
We may see an async-callconv helper like Await though. If it is possible to get here with those, it should throw. Also will need a test.