During upgrade or swap of an SCB on an MX router, chassisd crash might happens combined with core dumps.

Check inventory log in the var/log/ and look for part/serial number to identify the type of the CB/SCB: 

 00:46:44 CB 0 - part number 750-031391, serial number s/n

 00:46:46 CB 1 - part number 750-031391, serial number s/n

 00:46:48 CB 2 - part number 750-031391, serial number s/n

 00:25:37 CB 0 - part number 750-070866, serial number s/n

 00:25:40 CB 1 - part number 750-031391, serial number s/n

 00:25:55 CB 0 - part number 750-070866, serial number s/n

 00:25:58 CB 1 - part number 750-031391, serial number s/n

 00:26:08 CB 0 - part number 750-070866, serial number s/n

 00:26:12 CB 1 - part number 750-031391, serial number s/n

 00:26:21 CB 0 - part number 750-070866, serial number s/n

 00:26:25 CB 1 - part number 750-031391, serial number s/n

 00:43:09 CB 0 - part number 750-070866, serial number s/n

 00:43:12 CB 1 - part number 750-070866, serial number s/n

 00:43:14 CB 2 - part number 750-070866, serial number s/n

 00:53:47 CB 2 - part number 750-070866, serial number s/n

 00:58:43 CB 0 - part number 750-070866, serial number s/n

 00:58:46 CB 1 - part number 750-070866, serial number s/n

 00:58:48 CB 2 - part number 750-070866, serial number s/n

 01:06:40 CB 2 - part number 750-070866, serial number s/n

This might happens if there are SCBs compatibility issues on dual RE/CB MXs

Link to SCBE3 compatibility:

https://www.juniper.net/documentation/us/en/hardware/mx960/topics/concept/scbe3-desc.html

"The SCBE3-MX does not interoperate with any previous generation SCBs (SCB, SCBE, and SCBE2). Smooth upgrade is not supported."

Chassisd keeps crashing with core-dump

install compatible SCB model