ICX7250 switch gets out of sync with NTP server

[junghyun]

Hi

We are using 8 ICX7250 switches
Two of them are connected to the external network and six are located at the bottom of the firewall.
It is already connected to the internal NTP server, but the following log appears and the ntp sync state is observed to be released.
"the system clock is not synchronized to any time source"
We added 3 external NTP servers to solve the problem starting with 2 externally connected switches.
And when I debug, I can see that NTP packets are coming and going, but the offset is widening and sync is lost.
So, if you disable the ntp server, set the time manually, and try to synchronize with the ntp server again, it will remain in sync for a while and then the same symptom will repeat after a day or several days.

Is there any way to solve this?

The log visible in debug is as follows:

NTP: ntp_peer-unfit: dist exceeded - root dist 3.98533496 of peer 52.231.114.183 ha exceeded max dist 1.50096000

NTP : ntp_clock_filter: Adding offset -0/03647302, delay 0.00221265, disp 0.00001541 to filter[4] for peer 52.231.114.183

NTP : ntp_clock_filter: popcorn spike 0.00114024, ignoring new sample

After re-synchronizing, the sync status is fine right away.
The reach value also shows a value of 377 or nearby.
However, if you check after some time, you will see that the sync has been resolved.