I’ve seen a few threads with amazon links where the onebox is blank, for example Connectors for Star Topology CAN - #20 by gixxy
It looks like it was fixed here: FIX: return an empty result if response from Amazon is missing expected attributes by jbrw · Pull Request #13173 · discourse/discourse · GitHub discussion here: Amazon link preview works here but not on my forum - #14 by Richie - support - Discourse Meta so hopefully only a discourse upgrade is needed.