Chain reorganisation

When two valid blocks appear almost simultaneously, the network later converges on a single branch. Blocks on the abandoned branch are discarded, and the transactions they contained return to pending — or vanish if they were replaced.

That is exactly the risk confirmation counts are meant to cover. One or two block reorganisations are normal on some chains; deep reorganisations are rare and count as an incident. The confirmation count required per network reflects that reality rather than a uniform rule.