Are you sure nothing you haven't changed anything?
Like accidentally changed the milk? rinse the kefir grains? used metallic dinnerware? Kefir grains can be a little fussy. And sometimes when they are moved out of their "comfort zone" they go through a shock period or cycle, then after a while they adjust and return to normal.
How long has your kefir grains been acting like this?
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Ed... currently munching on some kefir grains... and gulping down a glass of nice cold kefir.