We are also seeing similar error again:
Reading package lists...
W: GPG error: https://apt.releases.hashicorp.com focal InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY DA418C88A3219F7B
E: The repository 'https://apt.releases.hashicorp.com focal InRelease' is not signed.
Error: Process completed with exit code 100.
DA418C88A3219F7B (fingerprint E8A032E094D8EB4EA189D270DA418C88A3219F7B) is in fact actually the old key before it was rotated last month.
Not sure why suddenly it is being used again (to be fair it’s scheduled to be revoked on 24th April 2023), so I guess we should still trust the old gpg key (again)?