Was the "unconstitutional" provision slipped in by one of the republican opponents as a "bill-killer" under the radar, or were the pro-immigrant people just that stupid?
I really don't know.
The CW is that they were just that stupid, while their aides knew but hoped no one would notice.
Does that mean not one member of the 100 knew and chose to say nothing hoping it would damage the chances of passage? That's up to you to decide. Given there were over 600 pages, it's possible it wasn't noted. We're all aware most of the Senate didn't even read it. But did Sessions know? His staff DID examine the legislation. They could have missed it, or not.