’ -> '

There is nothing wrong with this sentence; but I think it's worth comment.

I myself, as a native speaker, educated, old, and well-read, would use (and prefer) the simple past: "wasn't a problem." The word "before" makes the sequence unambiguous.

Nevertheless, there are "grammarians" (neither elected nor appointed), who insist on the past perfect when the action--as in this case--was "continuous." In my view this is an overly fussy attempt to make logical the messy treatment of "aspect" in English, typified by the ubiquitous parallel: "I am writing" and "I write," which are sometimes interchangeable, sometimes not.

English sentences are not constructed according to rule--except by students. Fluent speakers construct sentences according to pattern. Good grammarians discover and elucidate the patterns. Bad grammarians repeat without thought what they have been taught.

It is insufficiently appreciated that reductions to rule are not unique: there is more than one self-consistent way to do it. I have no doubt that counter-examples to this particular rule abound--and not just in my own speech.

To compound the confusion, I should prefer the past perfect if "before" were changed to "until." Why? I'm not sure. What comes to mind is that "until" sharpens the divide between before and after, and therefore calls for tense differentiation in a way that "before" does not.