This is the closest answer to your question on the forum, but James was answering to my question about storing sealed bags, not opened ones.
I would suggest you find somewhere cooler to store your Huel.
As for the open bags, there’s probably been some degradation of nutrients, but as long as no moisture at all has got inside the bags, they will be fine.
Does the powder taste and smell ok?
Is there any sign of moisture / condensation inside the bags?
Does it taste and smell ok?
How long have the bags been open?
As long as it seems ok, I would personally drink it!
If it smells or tastes ‘off’ it’s probably best to chuck it…
It’s probably ok though but possibly slightly less nutritious