Does Hillary Clinton have a second server and why hasn't it been seized?

If Platte River Networks is to be believed, there must be a second server. Why hasn't the FBI seized it?

Via Fox News:

The tens of thousands of emails on Hillary Clinton’s private server from when she was secretary of state could also be on a second device or server, according to news reports.
The FBI now has the only confirmed private server, as part of a Justice Department probe to determine whether it sent of received classified information for Clinton when she was the country’s top diplomat from 2009 to 2013.
Platte River Networks, which managed Clinton’s server and private email network after she left the State Department, has indicated it transfer – or “migrated” – emails from the original server in 2013, according to The Washington Examiner.
However, Clinton, the front-running Democratic presidential candidate, has suggested that she gave the department 55,000 pages of official emails and deleted roughly 30,000 personal ones in January, which raises the possibility they were culled from a second device.
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