Actually, fishing for that link, I see that a whole bunch of changes
was made to the CODEOWNERS file just recently:
https://github.com/zephyrproject-rtos/zephyr/commits/master/CODEOWNERS

Just imagine that any of those changes could break syntax a bit or
propagation of changes to it could glitch on Github side, leading to
the effect we see.

2018-08-31

Dear [github] support,

 

I’ve discovered what I believe to be a bug in CODEOWNERS. In particular, a single line failing to parse [trailing # comment] causes the entire file to stop identifying codeowners. This is in contrast to .gitignore, in which a single line failing to parse simply causes that line to be skipped. [...] I verified this behavior by making a sandbox repository and making pull requests until I narrowed down when the bug occurred [...] This situation was exacerbated by a lack of error messages in the GitHub UI. Ideally, we’d have access to a linter or at least highlighting in GitHub that would call out invalid syntax. 

Thanks for reaching out! This is currently expected behavior, but I can definitely understand why it would be unexpected. I’ll pass your feedback along to the team internally. I can’t say if or when a change will happen, but your feedback is in the right hands.