Huber was appointed originally in November 2017 and the FISA-related investigations were tacked on at a much later date.
On November 22, 2017, Sessions sent a letter to John Huber tasking him with reviewing issues that Congressional members had asked the AG to investigate. Attached to that letter were response letters that Sessions had sent to congressional members, which stated "This responds to your letters dated July 27, 2017, and September 26, 2017, in which you and other Members request the appointment of a Special Counsel to investigate various matters, including the sale of Uranium One, alleged unlawful dealings related to the Clinton Foundation and other matters……..
In order to determine what other investigations Huber had originally been charged with leading a team of senior federal prosecutors to investigate, we go to the July 27, 2017, and September 26, 2017, letters from Congress to former AG Sessions.
In the first letter, signed by 20 members of Congress, they asked a Special prosecutor be appointed to investigate items they believed Special Counsel Robert Mueller was not investigating, calling them a "plethora of matters connected to the 2016 election and its aftermath," unrelated to Russia interference, including "actions taken by previously public figures like Attorney General Loretta Lynch, FBI Director James Comey and Former Secretary of State Hillary Clinton."
Those issues, as stated in that letter, include:
1) Then-Attorney General Loretta Lynch directing Mr. Comey to mislead the American people on the nature of the Clinton investigation;
2) The shadow cast over our system of justice concerning Secretary Cliton and her involvement in mishandling classified information;
3) FBI and DOJ's investigative decisions related to former Secretary Clinton's email investigation, including the propriety and consequence of immunity deals given to potential Clinton co-conspirators Cheryl Mills, Heather Samuelson, John Bentel and possibly others;
4) The apparent failure of the DOJ to empanel a grand jury to investigate allegations of mishandling of classified information by Hillary Clinton and her associates;
5) The Department of State and its employees' involvement in determining which communications of Secretary Clinton's and her associates to turn over for public scrutiny;
6) Wikileaks disclosures concerning the Clinton Foundation and its potentially unlawful international dealings;
7) Connections between the Clinton campaign, or the Clinton Foundation, and foreign entities, including those from Russia and Ukraine;
8) Mr. Comey's knowledge of the purchase of Uranium One by the company Rosatom, whether the approval for the sale was connected to any donations made to the Clinton Foundation, and what role Secretary Clinton played in the approval of that sale that had national security ramifications.
9) Disclosures arising from unlawful access to the Democratic National Committee's (DNC) computer systems, including inappropriate collusion between the DNC and the Clinton campaign to undermine Senator Bernie Sanders' presidential campaign;
The other five issues addressed include what Comey and Lynch knew of president Trump being wiretapped, Comey's reliance on Fusion GPS, Comey leaks, and the unprecedented amount of "unmasking" of individuals on the trump campaign, transition team or both by Comey, Lynch, Susan Rice, Samantha Powers and others.
Note: Some of these issues are will possibly be addressed in the upcoming IG report to some extent, which any criminal referrals will then be handed over to Durham,but any that is outside the IG's scope in his investigation that are not handed over to Durham will fall under the purview of the Huber investigation.
The September 26, 2017 letter focuses on the premature exoneration of Hillary Clinton, before she and other witnesses had even been interviewed by the FBI.
Both letters can be seen here (PDF).
Because of the overlapping investigations, Durham and Huber are working in direct coordination with the DOJ's Inspector General's Office, which is why both are awaiting the final report, along with any criminal referrals may be attached.
The Epoch Times highlights another interesting detail in regards to the Uranium One investigation: "Notably, Uranium One had significant holdings in Utah, where Huber is based, including a small town, a uranium mill, and more than 10,000 acres of uranium claims."