It says in Shulchan Aruch, Even Haezer 62:8:
וי"א דשבת וי"ט ראשון ושני הוי כפנים חדשות בסעודת הלילה ושחרית אבל לא בסעודה שלישית:
some say that Shabbat and Yom Tov the first day and the second day are panim chadashos ("new faces") at the meals of the night and morning, but not the third meal
This is according to the Machaber. The Rema adds that the custom is to be lenient at Shalosh Seudas and make Sheva Brachos without new people, either because it's usual that panim chadashos do in fact come or because some sort of Drush or Divrei Torah are said and that's like panim chadashos.
Although the Shulchan Aruch says that Shabbos and Yom Tov Rishon V'Sheini can serve as panim chadashos, does a reason exist why one wouldn't need panim chadashos at a Sheva Brachos on Chol HaMoed?
Does anyone speak about this?