On Mon, Jul 10, 2017, 10:38 PM Eli Zaretskii <eliz@gnu.org> wrote:

When you say "line numbers disappeared", do you mean as if you set
display-line-numbers to nil, i.e. the text starts at the left edge of
the window?  

Yes. Exactly. And they reappear automatically too once that window is in focus again. 

I enable the line numbers via only major mode hooks, for some major modes. I am not 100% sure but each time this has happened, probably one window had a buffer with a major mode where the line numbers should be enabled, and the other didn't (I normally work in a 2-window frame). But also, I have never been able to recreate the problem.
--

Kaushal Modi