But it's not unreasonable that the certificate-in-question is indeed a root CA: all machines (not just this specific Verifone model) will error-out on an expire

But it's not unreasonable that the certificate-in-question is indeed a root CA: all machines (not just this specific Verifone model) will error-out on an expired end-entity certificates and the same can be said to intermediates (assuming that they don't issue directly from root). I've checked the original post where they're talking about this and it mentioned a server certificate so unless that machine choked on ECC certificates (possible but considering that no-one in the banking industry has encountered it as the error and the solution is a firmware upgrade, not that the server must back out of ECC deployment or apply dual ECC/RSA capabilities), speculating that this is something that other than root certificates doesn't align out with reality.