The incoming unconfirmed transaction from Tumbler to wallet A may not be the only unconfirmed parent of the transaction to wallet B.
It may have an unconfirmed parent as well.

If you're willing to use a blockexplorer to see the "effective fee rate" of all the bundled unconfirmed parent and children transactions,
Use mempool.space and search using the txid of any of the transactions.
There, you'll be able to see if there are even more unconfirmed ancestor transactions and the important effective fee rate of the CPFP txn bundle.
Click "CPFP !" to see how many unconfirmed transactions are bundled with yours.
If there are lots of transactions in the list, that's the cause of the issue and performing an expensive CPFP to the last transaction is your solution.