Now, a few thoughts as to your other notes to ponder…
If your roast tastes chocolately in milk but is a little bitter as espresso, that is most likely your roast depth (how dark you took the roast). This can always be a little bit of a trade off. To get strong, chocolately coffee you sometimes need to go a little darker (just into second crack), but this will also change the flavour of black coffee. Depends what you prefer to drink. Are you aiming for ideal espresso? You might need to settle for slightly milder white coffee by dropping you beans 1-2° earlier (yes - only that little!).
But changing beans can help -*I've always found that a slow, even lightly roasted Brazil gives a good hit of cocoa without having to go dark The Waghi is a beautiful, caramelly bean, that likes just before the start of second crack IMHO – you treat it gently you will be rewarded with caramel milkshake flavours, without the need for sugar
Grassy taste? I have heard that cupping description, but never really experienced that myself. Allowing the beans to age a bit more may help.
But that's doesn't really sound like acidity. A too-fast roast will give a front-of-the-tongue, licking a lemon flavour. A good acidity (as you gently slow that roast time down) will give a nice, back-of-the-throat zing like the final bite into a sherbet lemon. And to further complicate things – some beans have more or less acidity naturally. I think Waghi is pretty mild.
Your raw/grassy/lack of flavour may be the flatness I mentioned before - not a lot happening flavour-wise. I would think this could be (combined with your profile) the sign the roast has been a little bit long and has muted everything.
Idea for next time – use the same beans, try to speed up the time to first crack by 1-2 mins, keep first crack-second crack technique/time the same, but drop 1-2° earlier.
Any let us know what happens!