Hi Mahdi,
I think workarounds will be needed to deal with an unanticipated problem, so in this respect you may look at it as an "unknown-unknown" that calls for a corrective action to «work around» that problem.
However, what if you have a known-unknown, so the risk has been identified, and possibly accepted (as part of the response strategy), but then it turns out that some corrective action is needed? I would say a workaround would also be needed in this case.
My 2 cents here. I'll be glad to hear what others think about this.
Gabriella