17C is most of it. Yeast slows right down in a cool room and the one to three days people quote assumes somewhere in the low to mid twenties. In a cold kitchen the same batch might want five or six days, and you opened at three and let the pressure out.
Find the warmest spot you have, an airing cupboard or on top of the fridge, and give it longer. Also use the bug a few hours after feeding rather than days after, which is when it is at its most active.