I've confirmed that you're not using latest version, see source data:
In your source code following line is not included
<div itemprop="itemReviewed" itemscope itemtype="http://schema.org/Thing">
In latest version 1.1 I've changed schema.org markup code and added this to validate it. Please check once again, I've checked it on 3 different sites and plugin working without any problem,
Check this URLs in Rich Snippet tool:
Last one is testing site so I'm not adding URLs here.
I've added review markups on 12-15 posts, above are two samples for your reference.
Let me know if you've any further issues. Thanks for using my plugin.