Yep, @Jason M is right, this is a StudioPress plugin so they’ll be the ones who will be able to fix any issues with it.
Make sure and let them know it’s a PLUGIN issue and not a theme issue or they may send you back here by mistake.
Although, I personally wouldn’t be too concerned about it. Your site looks perfectly fine, and I don’t think it will affect anything like SEO, Performance, etc. I definitely don’t rely too much on Google’s tools, because they are not always 100% accurate.