Perhaps you tried to transact with a mempool much lower than the transaction fee currently required to transact Bitcoin, which is why your transaction is having this issue. The mempool may have been too high at the time you tried to make a Bitcoin transaction, but on the other hand, you may have tried to make a transaction using too little mempool due to which your transaction may not have been completed. It would be best if you take a screenshot of your transaction.
I left the mempool dial where it was which was to the far left as possible, I didn't fiddle with it at all, are you meant to always adjust that dial?Perhaps you tried to transact with a mempool much lower than the transaction fee currently required to transact Bitcoin, which is why your transaction is having this issue. The mempool may have been too high at the time you tried to make a Bitcoin transaction, but on the other hand, you may have tried to make a transaction using too little mempool due to which your transaction may not have been completed. It would be best if you take a screenshot of your transaction.
How does one gauge where to adjust the mempool dial to, like should you leave it midway or to the left? How will I know what the standard mempool fee is so then go back and adjust the dial on electrum just before pay button. 
