My father used to put a pinch of salt in his fresh ground coffee to remove bitterness, would this work with coffee flavoured Huel? May be worth a try.
I am hesitant. But I’ll try for sure. I am open for all ways to ‘like’ Huel. 
I found coffee Huel the worst tasting (my personal favourites are original with chocolate or mocha flavour) because of the bitter aftertaste you’d mentioned.
And yeah, definitely leave it in a really cold fridge overnight; makes a world of difference!
I have 2 scoops (one Vanilla, one U/U) in 700ml of water (400+300). I shake it up then leave it for an hour or more. I’ve not tried the coffee flavoured - one can always add coffee to Vanilla or U/U.
Glad to know that it isn’t just me. I am planning to do the same, original with the chocolate.
Coffee flavour will make me loose my love for coffee. 
Try making it with more water also.