Customer experiences continuos backup kernel crashes at a
production GRES enabled MX960 system running JUNOS release 21.4R3-S2.3 plus
JSUs:

Kernel crash issue has already been addressed under the previously known  internal PR1906842.

The crash path is deterministic: it always happens when a backup RE gets
IFSTATEs from master after a backup restart/startup or when previously
disabled GRES is re-enabled. The crash backtrace is the same in all the cases,
and the toxic IFSTATE the backup chokes on is also always the same: