What was your fee? I never have problems with Bitcoin Core's recommended fee, but i have had problems before when I was sending bitcoin from somewhere else... developers need to come together and make all wallets recommend the correct fee to avoid this annoying delay.
0.0001 as usual, never had any problems before even during previous attacks. Sent another with 3 times that, it went through as usual.
If you can post the transaction id, we can analyse what went wrong, maybe give you some pointers to avoid this problem in the future...
For example, the previous 3 times, you might have created a transaction with 1 input and 1 or 2 outputs, while this time you used 5 or 10 inputs and had 3 outputs (idk what happened, just an example). This might result in the first 3 transactions having suffient fees to get the transaction in one of the next couple of blocks, while this time, it has unsufficient fees to be added to a block swiftly...
I have to agree tough that it's very unpleasant if something like this happens to you... Good luck
