> Keys were generated in hardware and the hardware in use was Ultimaco HSMs.

The plot thickens.

Broken HSM? Misconfiguration? Confusion? Straight up lie?

> Excel attached. The Ultimaco devices were used to generate the ECC, RSA key pairs for the issuers. They were not used to generate any other key material. But it doesnt look like the device is at fault.

> 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)

…

> an approved deviation to our usual KGC to test

The whole point of a key ceremony is that you're not going off-script and YOLOing random crap.

Reading further, it seems like they say they first generated some keys on-HSM, but then used 'test keys' (that were used to test wrap/unwrap of key material) instead by accident. Fishy.