Are you saying that there is a gate where A's property meets the public roadway currently and the new owner of A wants to put a fence where your easement ends and enters your property?


unless there is something saying he cannot put up a gate across his property he can fence his property and put up a gate.

you have no obligation to close the gate though, unless he has animals.


yes, it would be simpler for him to leave the easement unobstructed but it is his property and he can do anything he wants with it unless he inhibits your rights.