[j-nsp] ISSU offlined mpc - why?

[mike+lists at yourtownonline.com]

Hello,

     I did an issu upgrade on an MX240 with dual routing engines, going 
from 15.1R6 to 17.4R2, and I had reviewed the fine manuals particularly 
concerning advance steps to ensure nonstop routing and so forth. But 
during the upgrade (near the very end), the router did offline my MPC 3D 
16x 10GE, resulting in loss of routing for 5 minutes. According to 
juniper in their docs that state that:

"Unified ISSU is supported with Junos OS Release 17.4R1 for MX Series 
routers with MPC-3D-16XGE-SFPP"

     my expectations were that the card would stay online and there 
would be little to no operational impact, but this clearly wasn't the 
case. I am just wondering if anyone can tell me why this might have been 
the case and in the future what steps I would need to take to ensure 
this both otherwise stays on the air during a future software update?


Thank you.

Mike-