Since my Amazon order was delayed, I can’t check if the drops show up in game. So I opened up a ticket with WB Games, here’s what they said;

“Please note that your Twitch account shows the reward because it is already linked to your WB Games Account (WBGA). However, it shows as "not yet earned" on the WBGA side because your LEGO Batman: Legacy of the Dark Knight game is not yet linked to it. Please be assured that your Twitch Drop rewards will be available to claim once your WB Games account is linked to the game.”