Sorry, I found the question but not much firm on an answer.

Here's the mention of it I saw on Facebook:

Schumer threatened to take away his Senate committee positions if he didn't concede, etc. He would have been ineffective in the next two years. I also personally believe that his family was threatened but there's nothing except the Clinton body count to justify my position. His Secret Service protection was also yanked.

And here's what Politico provided on the subject on 5/20 - the term 'fix' can be understood in several ways of course:

Democrats turn to Schumer to fix Sanders rift

Here's how Politico outlines Schumer's connections to both candidacies:

The future Democratic Leader has much riding on Clinton’s candidacy. Schumer has had a rocky relationship with the Obama White House, one that became more strained after he refused to back the president’s Iran nuclear deal last August. If Clinton assumes the White House next January, the longtime New York senator would ascend to a party leadership role with an ally to work with in the Oval Office.

But Schumer also has longstanding ties to Sanders — both senators are sons of Brooklyn, with the accents to prove it, and were fellow students at James Madison High School in Gravesend. Schumer also helped recruit and coach Sanders for his Senate run in 2006 — and it was Schumer who lured the populist Vermonter to the gilded Democratic donor retreat in Martha’s Vineyard for the annual Democratic Senatorial Campaign Committee fundraiser last year, according to insiders.

snip

Schumer has another Sanders connection: a longstanding relationship with Sanders’ senior strategist Tad Devine dating back to 1988, when he was a congressman serving on the convention rules committee and Devine was lead rules committee negotiator for nominee Michael Dukakis.

So, he's got history/cred with Bernie. Got it. (Bernie was ahead of Schumer in high school by a few years.)

The article only suggests but does not take the theory all the way home:

Schumer...has assiduously avoided dropping even one public note of concern or critique about Sanders. “Schumer is going to be leader and he needs Bernie to be helpful and listen to him, not be a bomb-thrower when he gets back to the Senate,” said another Schumer ally of his resistance to publicly criticize his colleague.

At the same time, Sanders needs Schumer: as the likely next Democratic leader, Schumer would have the clout to help determine his future role and power.

“I will play whatever role either campaign wants me to play to be helpful,” Schumer said in a diplomatic statement Friday. “I know Bernie -- he’s a very good, thoughtful person and he will play a constructive role.”

From C-Span

JUNE 9, 2016
Senator Chuck Schumer on Meeting with Senator Bernie Sanders Senator Chuck Schumer (D-NY) spoke to reporters following a meeting with Senator Bernie Sanders (I-VT), a candidate for the 2016 Democratic presidential nomination.

JUNE 9, 2016
Senate Minority Leader Reid on Meeting with Senator Bernie Sanders Senate Minority Leader Harry Reid (D-NV) spoke to reporters following a meeting with Senator Bernie Sanders (I-VT), a candidate for the 2016 Democratic presidential nomination. Senator Sanders had also met with President Obama and Vice President Biden earlier in the day. Senator Reid said that he respected Senator Sanders and the vitality of his campaign. He said that he would not urge Senator Sanders to follow any course of action.

This is MSDNC a year ago - portion about Bernie starts about 4:30 to about 6:00

JUNE 22, 2016
Senator Bernie Sanders 2016 Presidential Campaign Senator Bernie Sanders (I-VT), a 2016 Democratic presidential candidate, talked about his life and career. He spoke about his presidential campaign and progressive message, as well as the potential for endorsing Hillary Clinton. He also talked about Republican presidential candidate Donald Trump, saying he “is unfit to be president of the United States.”