Simple child theme modification but links are broken

I think your problem may be similar to this question: How could child theme be different than parent theme if I haven’t made changes?

When you activate a child theme (assuming it’s properly setup), you will inherit all of the parent theme’s styles (and usually widgets), but you will not inherit:

  • Menu assignment to theme locations
  • Theme options (sometimes, but I seem to recall Elegant Themes is an instance that doesn’t inherit options).

Hence, you’re probably seeing the expected behavior, and it’s not a problem with the child theme or WordPress, but rather a change in settings stemming from a new theme being activated.