Dont worry, because sooner or later they will fill up your transaction. I have always been worried because of the same, i have been using coinbase for a long time to send funds to my ledger.
Still sounds like Coinbase is waiting for the fiat to clear. If there's no txid then they haven't done the BTC transfer yet. Coinbase is pretty reliable.
A lot of times they use to take more than one hour or two in order to send the payment, it is still showing the transaction on your tx history, but there is no record of that tx, not even in the blockchain.
but sooner or later they will send out the transaction, there is nothing to worry about that. If it doesnt happen in less than 12 hours, then you are fucked.