Highly unlikely. More likely the leylandi has either been trimmed too hard at some point (they won't regropw ifd you cut into deeper than the leaves or it has a red spider mite infection

Try cutting all the bindweed off at the base - this probably involves some unpleasant crawling about! Then watch for new shoots and glyphosate them as they appear. Its a bore but worth doing as its likely to spread to other parts of the garden. If you mean that the front of the hedge is brown and bare it will nor green up again and you might consider planting other shrubs in front of the bare parts. I have a viburnum tinus doing this vary effectively.

Thanks very much for replies.