This error is caused by the Microsoft UAC (User Account Control) prompt requesting access while installing a product through the Epic Games launcher. If you ignore, don’t see, or deny this request, the install will cancel and result in this error. You should be able to solve the issue by Resuming/Repairing the associated product installation and clicking “Yes” when prompted by the UAC.
And yes, it’s completely ridiculous that it wasn’t coded to wait for your response.