Each node has its own mempool with its own memory limit (300MB, 1GB, etc). Transactions also take some time to propagate between the nodes, so even same size mempools may have slightly different content.

Maybe check https://mempool.space (possibly over Tor) to see if the original tx-id is still in their pool. But what matters more is whether the original tx is still in the mempools of mining pool operators.

@wiz of mempool.space announced a Transaction Accelerator project but I don't know if it has come online yet.

Bitcoin Core devs are working on "package relay" to help the underpaying txs into the mempools together with their high-fee child, but work is not yet complete.