tldr this is why it's recommended to wait at least 6 confirmations. 2 block splits are pretty rare afaik but have likely happened before. 1 block splits are more common. It's rare but bitcoin's design anticipates these splits and deals with them.

Some miners (A) were oblivious to (or ignoring) the substantial progress of other miners (B) for a period of time. If your node was only getting blocks originating from miners in (A), you might've accepted a payment that was spent again (ie double spent) on (B)'s chain. Meaning, its possible the payment you received on chain (A) is not valid from the POV of Bitcoin which is following chain (B) because it has more work than chain (A).

The page lists double spent transactions at the bottom which are probably mostly rbf'd txs.