Drains can be a cause of filth flies.
When cleaning, it is important to get to all the out of the way places. Why is that important, because bugs are going to hide in areas where it is dark and has lots of food potential. This drain has serious and potential problems just waiting to happen, filth flies are just one that could cause a serious and buggy problem. . The problem is that the water pipe is broken and allowing the water to drip outside the drain box. If this is the soda machine overflow pipe then all the sugars are going to cause even more issues. Time to get into the mess and fix it properly.