Lip ties are treated based on being symptomatic. They are usually not checked for, because they do not typically cause the same type of issues with nursing as tongue ties do. One baby can have a severe lip tie, and another can have the exact same positioning of the tie, and one baby can have issues and another will have none. It also has to do with how flexible the lip still is. My son has a lip tie. It cause some issues early on, like a shallow latch which I was able to correct, and really super frequent feedings. Some babies and mamas have much more serious issues though.Everyone has some degree of tissue there, it just depends on how able it is to stretch and where it attaches onto the gums.
Typically a lip tie won't cause a newborn not to latch. It'll cause them to latch poorly, painfully and have poor milk transfer though.
More common with babies who will not latch or feed at all after birth is babies who had to be born by csection(usually emergency csecs after long tiring labour), who's mothers had a lot of medications during labour, or babies who were born really traumatically during extremely long stressful labours. These babies are too exhausted or medicated to latch sometimes for the early days. Being premature is a big one too. Physical issues can cause it as well but are less frequent. My nephew couldn't latch after birth(traumatic emergency csec and lots of drugs for mom). My SIL ended up doing combo feeding but actually nursed at least occasionally until almost 17 months. All babies eventually come around and if they are physically unable to nurse, they might get a tube for a little while until they get stronger.
