@Eyespyauto,

Your assumption is most likely correct, we always recommend placing your powerline connections on the same circuit.

Most modern power breakers have a noise filter or other protections added for safety, however, these will either severely degrade or eliminate the powerline connection. There are other options that you can use, such as running ethernet cables under neath the ground, wireless mesh/extenders if your barn is close enough. Or you could potentially look into Point to Point Access Points(these are usually business class devices)