I can only thing of one instance in which merging post mix coins could create a near deterministic link, which would be if you sent a single UTXO to an empty wallet, coinjoined for a single round, then swept the resulting UTXOs to cold storage.

This edge case correlation is prevented if you register a second UTXO (especially if the second UTXO is already private), remix any UTXO from the first round, or merge your coins in two separate transactions when spending.