Site title is duplicated in all pages titles

I am using the Enigma theme, and it looks marvelous. However, I am struggling with a strange behavior: the site-title that appears beside all the pages title is duplicated; for example, my site title is “GIS+”, when I go to “Contact Us” page, its title in the browser appears like this: “Contact Us | GIS+GIS+”, whereas the correct title should be “Contact Us | GIS+”, and I face this problem with all the site pages. What might be the issue here? This is better elaborated with the screenshot in the link below.
My site URL: https://www.gis-plus.com
Screenshot URL: https://s3.postimg.org/6237ngmj7/Clip_948.jpg

Any help is appreciated,
Hani