I agree with TheMadScientist. Google has moved on, and they try very much to accommodate common technical missteps. The way I think they see this area is that ranking well should be based on the quality of content offered to the visitor, rather than technical precision. If they can find a way to sort it out, they do.
Does this mean you should make technical errors with no concern? not really - there is astill a chance you are making things difficult for Google to rank a site appropriately.
Correct a soft 404 if you can see that it really is a technical error - it could be the right step to take. But if it's not a source of trouble for you and there's only one occurrence. What I've seen as a common "soft 404" report from Google is that many redirects from truly different URLs point to the same content that returns a 200 OK in some way, even if that content doesn't actually say "not found".
Redirecting lots of URLs to the same category page can trigger the soft 404 report. And if you check your analytics you might well find that the traffic involved isn't doing you much good.