Below is a chart that shows the cash RBOB gasoline and cash ethanol prices (from Barchart) for the past few years. You can see that up until late 2017 changes in ethanol price more or less followed RBOB but lagged a couple weeks behind. In late 2017, it all changed. Changes in ethanol essentially became "uncoupled" from changes in RBOB.
Why? Well the answer is obvious if you look at the price of D6 RINS, they're 17 cents per gallon of ethanol or thereabouts. If you can sell a gallon of RBOB for $1.80 and it only costs you 1.7 cents (1/10th of one RIN) to get compliance why bother to add the ethanol.