Problem with math mode in markdown: equations get not rendered

[tsieger]

Some inline equations render well, but others do not. Consider this example:

this renders well:
$r_{ij} = \hat{\beta_j}$

this does not:
$r_{ij} = \hat{\beta_j} X_{ij}$

which getrs rendered this way:

[dvorka]

Reproducible, however, I leave math rendering on MathJax. I will check the version and whether all its modules are properly loaded...