This happened to me couple of times - borders would just randomly disappear in Chrome. All other browsers render them normally, but they just vanish in Chrome, on some screen sizes. Resizing helps sometimes, but I never was able to catch real pattern for reproducing.
If this ever happens to you, there is a (hacky) solution. Change border width from
border: 1px solid #000; /* change it to: */ border: thin solid #000;
Although I don’t like it, as it is a hacky workaround and I don’t really understand why it works, it does solve the issue.
It seems that I’m not the only one having this problem.