In debian packages for KEA 1.6.0, the provided default config file contain the following logger:

    "loggers": [
      {
        "debuglevel": 0,
        "name": "kea-dhcp4",
        "output_options": [
          {
            "output": "stdout",
            "pattern": "%-5p %mn"
          }
        ],
        "severity": "INFO"
      }
    ],

The pattern probably should be "pattern": "%-5p %m\n" instead. Same issue in DHCPv6 conf file.

This create unreadable logs in journald (missing line break)