I do mostly light roast espresso and I have battled underextracted espresso. I struggled more when I used a Mazzer. Now I use an EK43 and do 18g dose to 45g yield mostly and can only do 18g to 36g if the roast is a little darker. Yes, make sure temp is up, grind is fine, distribution right, use VST baskets and experiment with dropping the dose a little and if needed more yield from the dose. The reward is a very fruity and sweet espresso without those roast flavors (I don't enjoy those).

Which size vst basket are you using?

I have the 18g and 20g ridgeless. I sometimes used 19g in the 20g one especially with the Super Jolly. Now I mostly just use 18g in the 18g one and adjust grind and yield. Only reason I'm using the 18g is to cut down on the caffeine dose, not much less with 2g I might even try out the 15g one.