hmm...not so easy to say...it is like with baby or children and so...they all have there own way to learn and how fast they learn
maybe he was trained not well enough at the breeders, with a first name that the breeder did give it, and when they got there dog they did use a new one or one that was not easy to understand for the dog...or each one gives an other name or fun name...and poor doggy does so not know that someone wants soething from him-her

, or trouble with hearing could be also a problem... or to lazy to follow the Name...or to intelligent for its owner and knows one is calling but does think that there is no need to follow...or it is his-her breed....
(may i adk what breed this dog is

)
trump is an easy name you can call or shout over a field..but a dog with name like...quincallero or regalitz..does not work well
a vet can tell if he has a problem with his Hearing when the breeder id not do this already... and when all is alright, then maybe a bether training on the long leash or long rope with only one Name or a bether Name that the dog likes and follows^^