Kefir will change it’s taste and consistency through different seasons, changes in temperature etc. I don’t think anything is wrong with your kefir grains, perhaps at the same time the temp in your house was lower or something. I make it for years and have a lot of experience with it so for me this is quite normal. It is also explained by others, try reading Dom’s Kefir site, it has everything you ever wanted to know about kefir.
It is also normal for kefir to “separate” leaving whey at the bottom and cheesy part at the top. You just mix it up and it will be fine. If you ferment your kefir for 24 hours with the right ratio, it will be fine. I wanted to be sure so I ferment it for 36 hours and have different batches so I get one in the am and the other in the pm. I also ferment separate batch for my girls as they don’t like it that sour so theirs goes for approximately 24 hours.
As for the taste, it could range from something resembling yoghurt mixed with soda, it would have kind of a fizz, or it could be more sour like yoghurt,or even more sour than that. It’s all fine and good kefir.
Here is Dom’s site if anyone wants to read about it: