When logging into workbench I receive:
An error has occurred and you have been logged out: unknown_error: retry your request
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There is no trust site that I can find for workbench, but poking around the workbench menus turned up a help page that gives you a "report issue" link that takes you to a github issues page.
There is a specific issue for this occurance, https://github.com/forceworkbench/forceworkbench/issues/820 so I'd say that it's not just you.
The "answer" part of this answer is that there's not really anything you can do besides tracking the issue(s) on github (and that the source of information for workbench is github).
Expanding on Derek F's answer:
Since Derek posted the link, a user has posted a solution on that page:
This solution worked for me.