Hey! For me, I'm trying to think of it, and I can't really recall if this has ever happened to me. I don't think so, I don't really care how fluent I am, I can sometimes approach a stranger and ask a question being 100% fluent, sometimes not so fluent - but the final result in both ways is the same, I did what I want. But on the other hand, I think this has happened to me after an interview - but it wasn't my fluency, rather it was what I said, like I felt I could have phrased it better etc, but again, it was rather what I said that bothered me, not how I said it. But I believe what you've mentioned could be normal :)