It is a weird glitch where I cannot purchase deepsight weapons that I have not yet crafted even with sufficient spoils and inventory slots, with the only exception being 'Acasia's Dejection' legendary trace rifle as you can see in the linked picture. The purchase was blocked with the reason of "Not Enough Space" but it was clearly not the case because somehow I was able to purchase 'Acasia's Dejection' and not 'Nessa's Oblagation' which is in the same weapon slot.