While it's certainly possible that ISRG has been served a subpoena because it appears the US DOJ is now a mix of hacks and incompetent buffoons, it wouldn't matter because the whole point is that they don't know anything - what you told them is literally logged publicly for everybody to see without even knowing how to spell "subpoena" let alone issue one.

Some people have this insane idea that somehow the CA has some secret which either they minted and sent to the CA, or the CA minted and gave them a copy and so the US government could get this secret with a subpoena - but the whole fucking point of a Public Key Infrastructure is that we're using Public Key Encryption, if we were OK with everybody having secrets all over the place this entire thing wouldn't be needed.