Gary Illyes from Google said that having invalid schema markup does not hurt your rankings or your site. He said the worse case, if Google cannot parse the markup, it won’t use it.
Gary said this at the 10:56 mark into the SEO office hours video.
Gary was asked, “Can it hurt to have schema markup on a page that is invalid? (e.g. product markup without offer / review / aggregateRating)”
Gary responded, “Short answer is no. The long answer is also no, because if we can’t parse it, we just won’t use it. That might mean that you’ll miss out on some search features like rich attributes under your snippets though.”
So your click-through rate might suffer by not having those eye-catching rich results in the search results. But otherwise, rankings and other placements should not be impacted by having invalid schema markup.
Here is the video embed so you can watch it yourself:
Forum discussion at Twitter.