Northener here!
I add 3 scoops to 500-600ml water in the default shaker. No problems now; at the start I added the water to the Huel and that was too lumpy but for unknown reasons mixing it the other way solves this problem mostly.
I think the distinction between a gloopy sludge and a smoothie may be slender. Getting good nutrition in either form is good, compared to not having nutrition at all!