Weapon attachments change to lower tier

[Darkrow]

Anyone noticed that sometimes weapon attachments change to lower tier. I noticed that my pistol Unity 4+ had better tier silencer and scope (bought better attachments to replace the lower ones) and then some point it changed to tier 1 silencer and tier 2 scope (Weapon originally had those when i looted it). And it did not happen just one time but at least 3-4 times. And no it did not go to my backpack either looked it up. Annoying find out in combat that weapon does not perform as it used to and buying and replacing those mods many times and they are not free.