investigation was never closed, so it couldn't have been reopened, lol.
Here is a quote from a just released WSJ article re: the FBI investigation:
"These details on the probe are emerging amid the continuing furor surrounding FBI Director James Comey ’s disclosure to Congress that new emails had emerged that could be relevant to a separate,
previously closed FBI investigation of Mrs. Clinton’s email arrangement while she was secretary of state."
https://www.google.com/amp/www.wsj.com/amp/articles/secret-recordings-fueled-fbi-feud-in-clinton-probe-1478135518?client=safari