If you are using UE4.18 you can only use the branch 4.18. Over new engine releases, some changes in the Unreal API will force the code to be changed aswel to comply with those changes and they are meant only for that particular release. Sometimes we get a message in advance telling something will change in the next release and we should update it now and test, otherwise the next release compilation will fail. That said, only consider changing to newest branches whose name matches the UE4 release you are using.