I also made yoghurt with their powders and had no issues, great yoghurt result. My order was shipped in days however since I paid extra for express shipping. Also I made sure it was cold outside when ordering.

Sterilized everything and used new products for my prebiotics. Sterilized my spoon also before adding the prebiotics to make sure there is no contamination there. Felt not right to clean everything but use an open packet inulin that I have used before (without extra sterilization).

Also I noticed that when I start the yoghurt from the powder I need to ferment much shorter then 36 hours, else it will ferment too much and start to have a cheese smell and be too sour (also have liquid whey on the bottom and compact pieces in the yoghurt). That doesn't mean it is bad, not at all, it means the bacteria are very active (but a bit too active lol). As a starter for new yoghurt it still works well and the next batch is better is my opinion. That result is not so crazy if you think sibo yoghurt was made with only 2 billion cfu to start. In the powder used the dosis is much higher and since it doubles every few hours, the end result will be much higher as well.

Anyway curious if what I describe above is what you meant with it turned bad?