title-tag support

Hiya!

I’m using your great theme, but recently I’ve found out a problem with title tags.

Actually I set them up using Yoast seo, but in some post pages it duplicates the site name at the end of the title.

For example: Articlename – Sitename Sitename

Yoast says this could be related with title-tag support. Could you confirm it? Is there a way I could solve the problem?

Thank you so much for the help you can provide me ??

The page I need help with: [log in to see the link]