Report it if it's not accepted. However, just "yoghurt" without some is more common, as an unspecified amount. "some yoghurt" sounds like a small quantity.

The take-away here is that "des" (here) is simply the plural of "un/une". There is no true counterpart in English. Although some people use "some", it is almost always omitted in English. The French use it in plural here because they typically eat yogurt packaged in single-serving containers (100-125g).