Bluesky embed of leaflet with website embed captures screenshot too early (?)

In https://leaflet.pub/p/did:plc:j7nm3lrd5h7fm3sfhcv3lhfv/3mhefslbkoc2y it looks cool. On bluesky its captured a screenshot before the website fully rendered.

https://bsky.app/profile/larkworthy.bsky.social/post/3mheh43bzfc2i

I am wondering what signal leaflet/bluesky is using to decide when to take a screenshot. Maybe I can fix this if I understand it.