Fellow associated IBS person here!
My first three days on Huel (One 3 scoop meal per day) were a bowel revolution to put it politely. Having calculated how much more fiber I was now consuming compared to my previous eating habits I suspect that is what did it for me!
As soon as I started flavoring it and drinking it slowly with a thinner consistency everything settled down to just give a comfortably sated feeling.
Stick with it and I hope it settles down for you too!