On 27 October 2016, the disreputable Gateway Pundit web site published an article reporting that Robby Mook, Hillary Clinton's campaign manager, had deleted his Twitter timeline shortly after the FBI announced they were reviewing additional e-mails potentially linked to Clinton's use of a private server:
The entirety of Gateway Pundit article, reproduced above (with the exception of a video in which Donald Trump tells Hillary Clinton that she would be in jail if he were President), consisted of a catchy title, a baseless claim, and a screenshot of Mook's Twitter page. Gateway Pundit did not point to a single tweet that Mook had purportedly deleted or provide any evidence that his Twitter account was altered after the FBI's announcement.
The Gateway Pundit deleted their article shortly after publication (most likely because it was not backed up by any factual evidence) but, rumors continued to circulate that Mook had deleted his Twitter feed:
Wikileaks was also taken in by the rumor, although that publishing platform deleted their tweet shortly after posting it:
WikiLeaks just deleted this tweet about @RobbyMook, who just joined Twitter this week pic.twitter.com/9kQx7rBdXK
— Colin Campbell (@colincampbell) October 28, 2016
Robby Mook did not delete his Twitter feed because he was "spooked" about a potential FBI investigation into Clinton's campaign servers. Mook, Clinton's campaign manager, joined Twitter in April 2015 but didn't post anything to the service until 26 October 2016. The lack of activity on his account was not due to a cover-up; rather, it shows that he simply doesn't use the service very often.
An archived screenshot of Mook's page from May 2016, more than a year after his account was opened, shows lack of activity:
It should also be noted while the FBI's announcement in October 2016 may have been surprising to the Clinton campaign, controversy over the candidate's e-mail server was not. The investigation into Clinton's e-mails started in 2014, before Mook created his Twitter account and was a major focus throughout the 2016 Presidential election. The Gateway Pundit never explained why Mook would be "spooked" by the continuation of a long-running investigation or what he possibly could be hiding.