I had that happen too, with a single needle overlock stitch as well as two needle. I think it's needle type, some fabrics are very weak and sensitive to punch of the needle and thread, the tearing happens before there's any wear or force to the seam. The damage quickly excelerate and becomes more visible. I think microtex and jersey needle are recommended for this, it can make a difference, some of the girls here know this better than me.