This is so bad.
They're asking us to believe that a script flaw, on this specific day, for critical keys, silently generated a second, weaker key pair, and that the wrong pair was then used for the CSR because the labels looked similar. And "used by mistake because the labels were similar" means nobody checked the CSR's public key against the intended key before the root signed it. Worse, they had a direct signal months ago in Bug 1970728 their CRLs failed verification, and by their own account the fix was to re-sign with the flawed keys rather than ask why the "correct" keys didn’t match the certificates.
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> We have done some preliminary assessment, there appears to be a flaw in the KGC script that was used on that specific day to create these ECC issuers. As for these ECC keys, our review of the KGC, assessment of the code and view of HSM keys so far indicate that a) a set of original ECC keys were created onboard as expected b) an approved deviation to our usual KGC to test a wrap/unwrap was introduced as these keys were meant for export for this instance c) a flaw in the code resulted in the second pair of keys being created onboard which were weaker d) these second pair of weaker keys were used by mistake to create the csr (because the key labels were similar) and signed by our root e) the CSR from these weaker keys were also sent over to Sectigo for cross signing (we verified the files sent over to Sectigo)