This should be upvoted. Thank you, I hadn't realized that OP was referring to the heading font or scrolled down to see what is yes, quite a remarkable ligature. It appears to be Lato delivered from <https://brick.freetls.fastly.net/fonts/lato/700.woff> The ligature appears due to discretionary ligatures being turned on.

     h1, h2, h3 {
     font-feature-settings: "kern" 1, "liga" 1, "pnum" 1, "tnum" 0, "onum" 1, "lnum" 0, "dlig" 1;
      font-variant-ligatures: discretionary-ligatures;
     }