I made the usual 3 scoop Huel shake for lunch last Thursday morning before work. Got busy, had to get a train early and left it in the fridge. Went away for the weekend, back to work on Monday and had it for lunch then. Lovely.
I think temperature is important. There’s a kind of sourness that starts to make itself known after a day and a half or so. Definitely happens faster in heat - shaker bottle will make a pop sound when you open it and, eurgh.
Happens with every 'lent I’ve tried, fresh (or cooled overnight) is always beat.