our Sitelinks removed and some category page of our site removed form search results
I have read the FAQs and checked for similar issues: YES
My site's URL (web address) is: www.mihandownload.com
Description (including timeline of any changes made): from 21th of march to now
we have a famous website in Persian. its ranked 17th in Iran based on alexa ranking and we have near 500,000 visitor per day. in 21th of march we changed our template and we used HTML5 in the new one. we have used several h1 ags (sometime 10 h1 tag in each page because we have lots of sections) in HTML5 we can use H1 tags in each section.
unfortunately after changing out theme:
1- all our Sitelinks removed, also we can see site links in webmaster tools. please see this two picture:
It can but I am not sure that is the only reason that you would lose your rankings. From my experience anytime you roll out a new site design you loose a little in the rankings but you should be able to get them back. I would make sure that everything you changed is titled the same and your descriptions are the same. That could be one of the reasons that you are seeing the change in your rankings.
Its totally related to your new design. As you see in Google webmaster tools, sitelinks are making automatically and according to the structure of links on your website. I think after upgrading the template using HTML5, you made some changes in the links too and its th reason.