Chickens often get stuck on the inside of a corner of a fence, they can be moved out by pushing them around for a bit, however while they are in this corner it is difficult to click the chicken instead of the fence it is stuck in to breed it. The chicken will also not follow you if you are holding seeds. While the chicken is in breeding mode it is still unable to move around or to another chicken. Usually causing the two chickens left to not find each other and breed. The chicken will also not follow you if you are holding seeds.