Does anyone know why MathJax is adding the span element that causes the lines to be rendered to the right of all substituted statements? e.g. https://hepdata.net/record/ins1380234
This is a bug introduced in recent versions of Chrome. MathJax v2.6.0 includes a work-around for it, so upgrading your site to use the latest 2.6 version should resolve the problem. See the MathJax issue tracker for details.