Hi
Technically with 80 sign set of RSZ with just 4 bit known on MSB or LSB can use lattice attack to find target private key in seconds.
Its millions in 1 onc chance.

Only possible and known reason to have this is following.
It can be bug in tool which use to sign transaction which known from long time.
it can be self testing or very old address, old time they don't know much about nonce liner attack or weak nonce.

Regards,