I've been making yogurt for a bit less than a year, in a multicooker. My first starter was a single-serve cup of skyr, but since then I've just been using the last of the previous batch as the starter for the next. However, for the last few batches, I've been getting much more cloudiness in the whey when I strain it. The last batch, I got four times the volume of slightly-thickened-but-too-thin-for-a-strainer white liquid as I did of yogurt, which is enough loss to make me concerned enough to ask here. I saved the liquid (now jarred in the fridge), and left it to settle; a little normally-clear whey has separated to the top, but that's just the top quarter-inch or so of two pint jars that are otherwise full of white. Is there anything I can do to make yogurt or cheese or something from the liquid? Can the yogurt be salvaged to make good batches again, or will I need to start over with a new store-bought cup?
That happens sometimes, it means that the ecological balance in your yogurt has shifted to some less tasty bacterial strains. There is even a small chance that you picked up something slightly pathogenic.
There is neither a need nor a practical way to shift it back to the original strain. It is best to start with a new, known-good culture. You can get either store-bought yogurt, or pure starter from a type you enjoy.
You can expect this to happen again and again after a long chain of reinocculations, because in home conditions, you don't have perfect control over your fermentation process. It is just part of the life of a yogurt maker to get back to a fresh culture when the homegrown one weakens.