It’s natural ingredients, so there’s bound to be variation. I’m guessing it was either the pea protein or the rice that was in shortage as the u/u was also out of stock so couldn’t have been sweetener. And the gluten free was also affected which use different oats.
I know that if I buy two different brands of pea protein, the flavour can vary significantly. Same with rice powder.
It’s the same with all natural ingredients - take strawberries for example, or potatoes, or oranges, or tomatoes, or carrots. Buy from two different growers and the flavour can be completely different. If you only eat something occasionally, you are unlikely to notice the difference. But if you eat fresh raw carrots every single day, you would definitely notice straight away the difference in flavour when the seasons change or the supplier.
I’ve noticed as well with Huel, my taste buds become accustomed to the flavour and I like it more, the more I drink it. Any slight change in my own personal way of mixing it (filtered water / tap water from a different location / slightly different ratio of mix or of water etc) makes a massive difference as my taste buds are so sensitive to it.
Also, maybe anyone who went without for a while during the shortage, then went back to it. It would taste different just because their taste buds desensitised !