When using MathJax, apy seems to convert pairs of underscores to <em> tags, which makes the LaTeX code render incorrectly. Related issue:
lervag/apy#92.
Example:
# Note
model: Basic
## Front
Test 1
## Back
$\mathbb{R}_+$
# Note
model: Basic
## Front
Test 2
## Back
$\mathbb{R}_+$
$\mathbb{R}_+$
produces the following output:

