this member is called here

which this API is called from the public API TryWriteKeyValueSpanByte here

which takes ref SpanByte.

It is a GC hole since it's never pinned or otherwise fixed.

This is also a GC hole, since the memory is not fixed (you can also just use Unsafe.SizeOf here):

This is also seems to be a GC hole, since the memory is never fixed on this public API:

(note this list is not exhaustive)