It does look milky to me… good news is they flooded the inside with 40 so the “seal” is actually inside there and not actually on the seam itself where its milky. They may have set that sheet initially and it moved a bit during construction. Its good its on the bottom which is fully supported so it cant actually move or receive any pressure. If it were on an upright seam i might b concerned but i wouldn’t worry as is. Worst case scenario u have pictures and its under warranty but again not much or any concern as is.