It's not your node, but the software (ThunderHub, Zeus, etc) that derives the keypair from your node key. Zeus and ThunderHub probably implement lnurl-auth differently. They shouldn't but it sounds like they do.
Indeed, Evan confirm it. TH is using other signing endpoint.
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This is happening a lot. Apparently Alby and lndhub have similar issues.
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Do you think I should raise the question to Zeus guys or is normal behavior this?
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I would raise to Zeus. It's not normal behavior
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