If your client is a US citizen or Resident Alien they pay US tax on their worldwide income, whether or not they bring it into the US.

I'm not sure what "The client submitted Form 1065, but there was no income movement, so no amounts are recorded." means.

And their ownership in foreign entities may require filing of additional disclosure forms FBAR, 8938, 5471, 8865, etc. that carry hefty penalties. Also possible GILTI tax.