I don't know the piece, but I'd think it's something like a full cutoff or a complete break. If it's for separating the 8va's, it's kind of redundant. Then again, so is the 8va's on the lower staff.... I guess it's being a little sloppy or informal about notating it. I don't think those 8vas and the break are standard. At the least, I'd say it's a brief pause, like a breath, and then maybe a change of style/tempo, etc. It could be a full pause though too.