I think I know why, it's because of non-english character in folder name (I store my files in shared UNC path with non-english characters folder name)
For example you can change parent folder to something like ひらがな, then this error will occur.
Other button also have the same error, previously when using "Export scene...", I save to another path with all english chars so it works fine. Now if I save to non-english path, I can reproduce this error easily.
So I think it's not scene related or button related, just problem with save to non-english path.