Does the PH in your mouth affect taste?
I'm sure you have not expericed the same thing with products other than yoghurt. It is difficult to standardize the taste and consistency of yoghurt despite of climate controlled manufacturing facilities because there are numerous factors other than just temperature. Also, the milk is not always the same despite of homogenization process.

In other words, it's not your mouth, it's the product which comes out different every time. It is also the case with artisan wines.