Not applying time from NTP server

[Geving]

I have four devices, all have the same network configuration. Two of these units reports the date as early 1970, depending on uptime. This would be "normal" if the unit was unable to contact the NTP servers, but this is NOT the case. I noticed this problem on a fw version before 5.12.0, and also experience it on 6.3.x and 6.5.0 and 6.5.0.4. However, if flash the minimum version of 6.5.0.4, the device reports the correct time. If I flash back to 6.5.0 or 6.5.0.4, the device again reports 1970. I've tried both Core 2.4.2. and 2.3.0. based firmwares with equal results.