User may observe that the even number of ports are down after the upgrade (Example: xe-x/x/2,4,6,8,10..etc)
 

After upgrade the device from from 14.1X53-D27.3 to 21.4R3.15 the even numbered ports are down

• Check the interface status in show interface <> extensive, check is there any active alarm

root> show interfaces <> extensive

  Active alarms : LINK

  Active defects : LINK, LOCAL-FAULT

• Try to hard reset the SFPs and check the status
• Verify the interface optics-diagnostic in show interface diagnostic optics <interface name>
• Further, please perform softloop for one interface and check whether the interface is coming up or not, if the port is up then we can confirm that no apparent issue with layer 1 connectivity.
• Try to hard reboot the device by removing the power cable and connected back post that check the interface status by using show interfaces terse command output

If you still observing the issue, please open a Jtac case for further isolation.