Sourdough like gum
I used to be able to make good sourdough bread, recently though whenever I make the dough I will develop the gluten, I can make a windowpane, in a mater of hours the dough turnes into the consistancy of gum it is like the gluten has dissolved. I try baking th bread and it turnes out heavy and dense. this is a regular white flour and water starter. Can anyone give me an idea as to what am I doing wrong?