Hydrogen Embrittlement Test Failure

Q. Cause of hydrogen Embrittlement Test Failure?
Cadmium Plate:
ASTM F519 1a.1 Grade A.
ASTM F519 1a.1 Grade B

We have carried out a controlled batch testing in all process tanks and can exclude the following:
1) Impact damage of test specimens -- All test specimens were NDTs to assess for surface cracking both before and after processing
2) Corrosion of test specimens -- We have examined the test specimens which failed under magnification and there was no corrosion evident
3) Ineffective Heat Treatment -- Assessment of records along with monitoring of controlled batch showed evidence that best practise or correct process was followed & in place.
4) Material quality of test specimens -- The same batch of material was used for both pass and fail results. This however is inconclusive.
5) Modification to test specimen -- Standard practise across both pass and failed test results show this is not part of the root cause.