This is article explains how to deal with Management interfaces {em0) down issue in PTX series devices.

You will see the below.

Physical interface: em0, Enabled, Physical link is Down

 Interface index: 64, SNMP ifIndex: 17, Generation: 1

 Type: Ethernet, Link-level type: Ethernet, MTU: 1514, Clocking: Unspecified, Speed: 1000 Mbps

Check the interfaces status of both em0 and em1

> show interfaces em0

> show interfaces em1

If em0 is down, move the management connection em1 and check the status.

In the meantime also swap the em0 cable from Master RE to em0 port back up RE to exclude any cabling issue.

If the both the above doesn't give you required result, please reseat/reboot the RE and check the status of management port.

At last if nothing works, please process the RMA for the RE.

For More information on management interfaces refer below document:

https://www.juniper.net/documentation/us/en/software/junos/junos-getting-started/topics/concept/interfaces-understanding-management-ethernet-interfaces.html