DAG Not Always Generated on AMD 
I'm running into this problem on 290 and Vega 56 cards.  Sometimes the DAG is not generated when the miner is started.  And when it is generated, I don't know how to say this but it's like it loses the DAG.  The miner will still run but gpu usage goes to 0.  If I let it run it kind of generates it at some point and mining commences again until it loses it. 