Warning about `label` and `ref` linking failures and "Suppressing link with empty target" warnings

[augustfly]

AASTeX 6 is built on the RevTeX package, version 4.1, which is sourced in our adoption of emulateapj in 2015. revtex-4.1 is an outdated package, which is a fact that is leading to an increased number of conflicts with both core- and contributed-latex packages. This issue has spread to a core functionality: linking floats and equations with \label{} and \ref{}.

If you see the warning, "Suppressing link with empty target" thrown by hyperref, and you find that none of your \label{} and \ref{} links are appearing in your compiled PDF then the error is due to a conflict between revtex and latex.

One workaround can be found at latex3/hyperref#284