Sounds like the teat isn’t in properly. I’ve had the same mam bottles for 2 years and not had an issue
@sylvia they’ve definitely been in properly xx
@Stacey they’re definitely in properly it’s the first thing I checked
Have you taken them out to wash. I always find milk in the grooves so at every wash I pop them out and give the grooves a wipe. I wonder if there is a build up and it’s affecting the seal
Had this happen a few time on mine. Found either the teats wasn’t in properly or the teat was starting to need replacing. Hope this helps.