Could be that. I usually do 19-19.5g but was having better results with Monmouth using an 18.5g dose with a finer grind. Could have messed my settings up a touch. Will try with more.
That should be plenty in a double basket, but sometimes if you're using an auto grinder it can drop as much as a couple of grams over a period of time without you noticing, same if you dose by eye.
Has the dose dropped a little? Try increasing it and coarsening the grind a touch.