Some WP embed links no longer working aftter moving to FSE

Hey people of WP,

I’m retheming an existing site through FSE (2024 + custom). Client uses many WordPress link embeds from his own site. They work fine on his existing site, but on the FSE site some display and some don’t. I can’t figure out why this is. When I try re-embed the link via a block (embed or WP doesn’t matter) I get the error: “Sorry, this content could not be embedded.” I am baffled by this one, so any pointers will be much appreciated.

As a side topic – my understanding is that this is actually bad practice because of performance impact. I am considering offering my client a block pattern instead to populate when they want to highlight a post, but I’d still like to understand why this is happening.

Thanks so much.

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