https://www.theregister.co.uk/2018/05/25/cisco_admins_hold_that_ios_xr_update_while_you_get_new_firmware/

Eight Cisco NCS 6000 line cards need firmware upgrades, after Switchzilla learned they could be bricked by an IOS XR upgrade.

The operating system upgrade in question is IOS XR 5.2.x.