I initially thought this was the Clinton campaign doing what Trump tried to do to Biden: instigate an investigation of a political opponent. That would be illegal if they knowingly fed the FBI false information; if it really were a hoax.
The problem Durham has is the information is real. Inconclusive, but real. afaik, Sussman never suggested it was proof. It was just a suggestive lead. He hoped the FBI might dig deeper and find something.
My feeling is Sussman (and Baker) wanted to keep the source of the white papers out of it because it might adversely color the investigation. I am guessing they wanted fresh eyes looking at the evidence.
In the end, they looked into it, and found it was uncorroborated. Had Sussman told them he was representing a named or anonymous client; they would have looked into it and found it uncorroborated.