Spoiler: Ranking Drop

Hi everyone,My site just changed to a new domain (the domain is aged, have good metrics, clean, etc.) and the migration was done seamlessly, all 301 redirect done properly and use the change site tool on GSC too.On the first to seventh days since migration. Everything is fine. Even my traffic has doubled, because of better ranking than the previous site.A lot of keywords that sitting on 5-10 on the old site, sitting on 1-3 on the new site.But... everything has changed like 12 hours ago,You got the idea of how massive the drop was.Is it a normal thing if domain just changed? But from 1st to 7th days, everything is fine. I have no idea why it happened in just 2-3 hours, and my rank drops heavily.I checked on GSC both on my old and new domain, no manual action (thank God).Thanks, I hope you can help me to figure out what's the problem. And I hope it's just a temporary drop.