The article explains the PIC restart condition when you make speed change configuration on PIC

PIC bounces when configuring speed change on PIC level or specific port for MPC10E cards

Configured speed on the port level

The PIC restarted

It caused an outage for customers

https://www.juniper.net/documentation/us/en/software/junos/interfaces-ethernet/topics/topic-map/port-speed-mx-routers.html#id-port-speed-on-mpc10e10cmrate-overview

The document mentions the following:

"When you change the speed at the PIC level, the PIC restarts automatically with the newly configured speed. When you configure the speed of a port at the port level, only the speed of that port is modified. All other ports in the PIC remain unaffected. You cannot configure the port speed simultaneously at the PIC and port levels."

When we change the speed at port level, all other port in PIC remains unaffected - What it means is that only the specific port will have that speed change and other ports remains unaffected from the speed change. Document doesn't clearly mentions if the PIC will restart when we change the speed on port level, but as checked in lab, that the PIC restarts even if we make speed change on port level, (MX960 21.4R3)

Customer did another change on the port level and the PIC didn't restart this time because of the following condition:

The PIC restarts automatically when you change between modes on the router. For example, if you switch from PIC mode where all ports are configured with the same speed to a mode where each port can be individually configured, the PIC will restart. This applies to all the mentioned routers in the context, including the MPC10E-15C-MRATE, MPC10E-10C-MRATE, MX204, and MX304. The restart is necessary to apply the new configuration and ensure that the ports operate at the desired speed.

Reference: https://www.juniper.net/documentation/us/en/software/junos/interfaces-ethernet/topics/topic-map/port-speed-mx-routers.html