Error 503 in google webmasters for common mobile phones (smartphones are OK)

I really like the plugin and it helped me to get nice pages without errors for Smartphones, but I’m getting errors with code 503 for the Common Mobiles phones at Google Webmasters (site is working fine in both PC and Mobile mode, It look nice at my mobile and in Chrome and Mozilla mobile simulation, but I don’t know how to test it for the common mobile phone). It looks like I’ll get his error for all pages. I don’t know how to fix it and can’t find any info… Anyone has some ideas?

https://wordpress.org/plugins/wp-mobile-edition/