tldr; try supplementing your daily meals with three tablespoons of chia seeds.
For those experiencing a lot of loose bowels, etc from replacing more than one meal a day with Huel one thing that worked for me was supplementing my daily diet with about three tablespoons of chia seeds (not with the Huel).
Three tablespoons should be about 42 grams of chia seeds. Typically I mix it in with some juice or flavored tea and consume it throughout the day. Chia seeds has a tremendous amount of soluble fibers and mucilage pound for pound, and really helps with my digestion. Definitely not medical advice BUT it worked really well for me especially when dealing with some digestive issues when replacing more than 1 meal a day with Huel.