Google has revealed that some Chromebooks with Chrome OS v49 currently have a "critical bug" in their firmware updater, and the company has paused automatic updates for those devices until the issue is fixed.
The bug was first revealed in a post on the Chromium bug tracker stated:
There is a critical bug in the firmware updater that we are actively investigating which may impact few devices during an auto update: Lenovo N22 11.6, Acer Chromebook R11, Sanance / Chromebook 14, Asus Chromebook C300SA and ThinkPad 11e Chromebook. As a precaution, we have temporarily paused the automatic updates for these units until we are confident the problem is root caused/resolved. We should be able to resume automatic updates in the next coming days and confirm on this bug accordingly.
Thanks to Chad for the tip!