If you enter the title in SEO for a page, the name of website appears automatically. Example: 'Home | Justshop'
But after saving the page, that title might be seen duplicated like 'Home | JustshopJustshop'
So, to solve this issue, go to SEO > Titles & Metas and in the 'General' tab enable the checkbox as 'on' for 'Force Rewrite Rules'.
See image below or click here to open in new window