The quest items are not displayed in the backpack. (The Elder Scrolls 5: Skyrim)

I don't know how it all started, but quest items are not displayed in the backpack. What does it have to do exactly when they are needed on a quest. (If you spawn a quest item into your backpack before or after completing the quest, it is displayed, but during the quest the item is not displayed in the backpack. The console does not save - the item remains invisible). This happens not only with items from Skyrim, but also with items from mods.
Items are not displayed exactly. They are in the backpack, but they are not visible. (Example: on the Civil War quest, while hunting for the bone crown, we find an ebony claw. If you pick it up, it will not be in the backpack, however, when the door is activated, there is a corresponding animation and the claw opens the door.)
How to deal with this? Or at least what could it be connected with?