The JT may have issues renewing hftp tokens which disrupt long distcp jobs. The problem is the JT's delegation token renewal code is built on brittle assumptions. The token's service field contains only the "ip:port" pair. The renewal process assumes that the scheme must be hdfs. If that fails due to a VersionMismatchException, it tries https based on another assumption that it must be hftp if it's not hdfs. A number of other exceptions, most commonly IOExceptions, can be generated which fouls up the renewal since it won't fallback to https.