This was the second game we had loaded that day (on a Multiplayer server).
We played Funemployed, then switched to my custom version of Two Rooms and a Boom.
Both used custom decks.

The custom version had an infinite bag full of bags.
We took a bag and placed a card inside. When searching the bag the card appeared as just white rather than actually showing the image.
We weren't able to rectify this whether reloading the mod, spawning another bag in, or spawning a custom bag in.

EDIT: I was able to recreate this. Only seems to happen after loading the initial mod and bugs in both Singleplayer and Multiplayer.

This is what it looks like, the card should be a "Blue Team" card: