- did you dry hop this batch? If so, either dip tube or Out post poppet could clog - repeatedly. Noobs catch me with this one all the time because they never mention the dry hopping (nor the less than stellar racking ) Hence it's now my Numero Uno question.
- you have the end of the long dip tube slammed against the keg bottom.
Yes, that happens.
- the Out post poppet spring is too stiff for the spring-loaded plunger in the beer quick disconnect to displace. This isn't uncommon when "universal poppets" have been used, as some posts are too short for the "universal" springs, which need to have a loop or so cut off. It can also happen when someone cleans multiple kegs and gets the poppets mixed up (wicked bad juju)...