Why does Lydia keep switching back to her starter shield?

I've crafted a full set of armor for Lydia, but every now and again she'll revert back to her circular iron starter shield instead of the one I made for her. The only way I've seen to fix this is to trade with her, take the shield, and then give it back.

Is this merely cosmetic? If not, how can I stop it from happening?

Solution 1:

It's a follower bug where they refresh their inventory and re-equip their old gear.

If you have the relevant pickpocket perks, you can pickpocket their old gear out of their inventory.

If you have the console, you can delete their classic items out of their inventory with <refID>.removeitem <item ID> <count>. You can use <refID>.showinventory to list their "true" inventory of items (including the hidden gear).

Further reading:

• Skyrim Followers
• Skyrim Console