Dr brown bottles formula not coming to nipple

Hi everyone I was wondering if anyone had issues with these bottles ? They just started to where when my daughter drinks what's in the nipple no more will come out unless the bottle is removed from her mouth. It's not every bottle but 9 times out of 10 it's happening both with the green valves and the blue valves. She's on size 1 nipples. We tried size 2 and that was a mess.