The 2019-05-05 security update appears to have made a minor backwards incompatible change requiring an update to Auditor and AttestationServer. I need to determine which devices are impacted and I'll come up with a proper migration path that I can push out in a tiny release soon.
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This is fixed by github.com/GrapheneOS/Aud and I've released a new version of the Auditor app including this change. The compatibility issue was only with the Pixel 3 and Pixel 3 XL due to the TEE moving to the same sha256 verified boot key format as StrongBox (Titan M keystore).