I have a sheet metal box part that loses its references for seemingly no reason. If I change something anywhere else on the model (for example, cut extrude a hole through the bottom), the references break. The references that are breaking are tabs + sketched bends at the top of the model and some holes that are on them. 

In the sketches, points coincident to the tabs break the coincident relation, and the sketch planes (top face of the tabs) break as well. Every time I repair them, it breaks again next time I change anything completely unrelated afaik, and sometimes when I do a ctrl+Q rebuild it breaks. 

This is baffling to me and I hope I'm missing something simple.