NTP - Clock is not syncing to low stratum server

Question

Issue Summary

Open NTP - Version 4.2.6p3 - Clock is not syncing to low stratum server.

Issue Description

1. I am running a NTP Unicast Client in my Ubuntu system.
2. I have 3 servers, Server1-Stratum=13, Server2-Stratum=5, Server3-Stratum=4.
3. Clock is not syncing to Server3 rather it is syncing to Server1.

Queries

1. Whether this is a expected behavior ? Because as per my understanding NTP Client should sync to Low stratum server.
2. How NTP Daemon will decide server for sync, by configuration order or by stratum ?

Outputs of ntpq -np

Client

root@hmllab:~# ntpq -np
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
x172.31.112.136  LOCAL(0)        13 u   14   16  377    0.255  -27.571   0.340
x172.31.112.139  LOCAL(0)         5 u    5   16  377    0.211  -126229   3.221
x172.31.112.142  LOCAL(0)         4 u    5   16  377    0.160  -946075   1.078
root@hmllab:~#
root@hmllab:~#
root@hmllab:~# date
Wed Jan  1 01:46:06 UTC 2020
root@hmllab:~#

Server 1

root@hmlpc136 ~ $
root@hmlpc136 ~ $ntpq -np
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*127.127.1.0     .LOCL.          12 l   47   64  377    0.000    0.000   0.001
root@hmlpc136 ~ $
root@hmlpc136 ~ $
root@hmlpc136 ~ $date
Wed Jan  1 01:46:13 UTC 2020
root@hmlpc136 ~ $

Server 2

[root@hmlpc139 ~]#
[root@hmlpc139 ~]# ntpq -np
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*127.127.1.0     .LOCL.           4 l   13   64  377    0.000    0.000   0.000
[root@hmlpc139 ~]#
[root@hmlpc139 ~]# date
Fri Jan  1 01:53:44 UTC 2016
[root@hmlpc139 ~]#
[root@hmlpc139 ~]#

Server 3

root@hmllab-OptiPlex-3020:~#
root@hmllab-OptiPlex-3020:~# ntpq -np
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*127.127.1.0     .LOCL.           3 l   12   64  377    0.000    0.000   0.000
root@hmllab-OptiPlex-3020:~#
root@hmllab-OptiPlex-3020:~#
root@hmllab-OptiPlex-3020:~# date
Sun Jan  1 01:53:35 UTC 2017
root@hmllab-OptiPlex-3020:~#

Answer 1

Your ntpq -np is showing with the x at the start of the line that all three of your servers are falsetickers. Basically, none of your servers agree with each other, so none are chosen. See the discussion at ntp.org. You would be better off with one server!

Perhaps after a few hours your stratum 4 server will be chosen. Of course, the date may still not change as the time difference is too great. It depends on your config.