Friendly cc'ing @FiloSottile 🙏

This output mismatch could to be related to this commit: crypto/ecdsa: draw a fixed amount of entropy while signing.

You should not expect the signature value to be stable relatively to a specific randomness input stream. We actually go out of our way to draw an extra byte or not to not always generate the same signature, but since your randomness input is all zeroes, it will still look stable-ish. Anyway, the algorithm will sometimes change between releases, that's to be expected.

Thanks for the quick response & clarification! Although I need to get my head around your words as I don't understand how the same input could output different results and they continue to be verifiable! I will take a look to the verify internals. Thanks!

Unlike hashes, there can be multiple valid signatures for a (message, public key) pair. Some algorithms like Ed25519 are deterministic in that they will always generate the same one when signing, but that's just an implementation choice. You could add randomness to Ed25519 and get many valid signatures for the same message. If you need that not to be true, you want a Verifiable Random Function, not a signature scheme.

Thanks for the detailed comment @FiloSottile, it's really appreciated!