Bitcoin transaction unconfirmed, while way past expected processing time I have started a transaction from "wallet A" at 2017-06-14 11:51:40 with 


  Fees 0.00066328 BTC,
  Fee per byte 293.487 sat/B


Which is not yet confirmed over 8 hours later. 
I have a second transaction from "wallet B" at 2017-06-14 18:08:25 with 


  Fees 0.000599 BTC,
  Fee per byte 265.044 sat/B


Which was started almost 8 hours later than the first, with less Satoshi per byte and was confirmed within approx 1 hour. 


How can the first transaction, with a higher fee not be processed, while the second one is? I know I didn't choose the highest fee, but the selected fee should have processed the transaction within 3 blocks, which was supposed to be within 60 minutes according to https://bitcoinfees.21.co/.

Edit:

I do have a past unconfirmed transaction, for which I put a way too low transaction fee, on that wallet. If there is a previous unconfirmed transaction, does that mean the next transactions will wait for the unconfirmed transaction to complete? This will never happen...
That's correct, a transaction cannot be confirmed until all its inputs (and all of their inputs, and so on) have confirmed.  (It is allowed for the transaction to go in the same block as its inputs, so that they confirm simultaneously.)

You may be able to remedy the situation by creating a third transaction that spends the second (7da9), with a large enough fee such that the overall average fee of all three transactions is at or above market rate.  Miners may be smart enough to realize that they can earn a good overall fee by confirming all three.  This is the idea of the child-pays-for-parent scheme, though it's usually used to have a transaction pay for its immediate inputs; I don't know whether the software used by most miners would detect longer chains like this one.

You can also wait for a while until other nodes have forgotten the low-fee a762 transaction, and then try to replace it with a higher-fee transaction (a double spend).  The details of doing this depend on your wallet; often it involves "zapping transactions" or "resetting blockchain" so that the wallet forgets what transactions it created, and scans the blockchain to find only those which are confirmed.  If other nodes have also forgotten the unconfirmed transaction, then it's as if they never happened and you can start again.