The switch went offline with reason power cycle under show chassis routing engine command 

EX switch got rebooted unexpectedly

• Take the console access of the device and check what is the status of the chassis.
• If the device stuck in loader prompt then try to reboot the device.

          command: loader> reboot

• If there is no output in the console, please try to hard reboot the device.
• Once we are able to access the device check the health status of the rebooted device
• Is there is any core-dump, storage issue or high cpu please work on it before proceeding with next steps.
• Check the command file show /var/run/dmesg.boot.detail. if we are observing below logs in the command output, it indicates that issue is with file corruption.

UNKNOWN FILE TYPE I=636

UNEXPECTED

SOFT UPDATE INCONSISTENCY

CLEAR?

yes

UNKNOWN

FILE TYPE I=637

UNEXPECTED

SOFT UPDATE INCONSISTENCY

CLEAR?

yes

UNKNOWN

FILE TYPE I=638

UNEXPECTED

SOFT UPDATE INCONSISTENCY

CLEAR?

yes

UNKNOWN

FILE TYPE I=639

UNEXPECTED

SOFT UPDATE INCONSISTENCY

CLEAR?

yes

• Please perform format installation to fix the file corruption in the device

Pre-requisite for format installation :

• Need console access to the devices.
• Please take the configuration backup before the activity

             >show configuration | no-more

              >show configuration | display set | no-more

• Please have a USB sticks of 4GB or 8GB

Follow the KB article for format installation:

https://supportportal.juniper.net/s/article/EX-Performing-and-resolving-any-common-issues-during-Format-Install-on-legacy-EX-platforms?language=en_US
https://supportportal.juniper.net/s/article/EX-How-to-format-install-EX2300s-and-EX3400s-via-USB?language=en_US
https://supportportal.juniper.net/s/article/EX-QFX-Procedure-to-format-install-QFX5K-device-using-a-USB?language=en_US

• If the device still rebooting even after perform the format installation, please raise a JTAC case to check the issue further.