Problem: user adds a collectible/NFT to their wallet manually (with 'Add Collectible' flow), and the wallet starts to show the collectible. If the user closes the app, and reopens - the NFT is removed, and they need to re-add it.

Expected: once a custom NFT is added, it should not disappear when they relaunch the app. If they logout and login again, it should stay as well. It should only disappear if the user explicitly removes it.

Issue reported here: https://community.metamask.io/t/collectibles-in-metamask-app/620