Did your squigglies disappear?? Here's the most likely culprit.
I've been working a lot with MDX and I realized that the spell checker wasn't working. I wasn't sure if I disabled it globally. I re-enabled it, but that didn't seem to fix the trick.
Eventually I found that the issue was that
mdx was not in the list of languages that the plugin (
cSpell) was targeting.
Here's how to fix it:
You can find this in your user or workspace settings as C Spell: Enabled Language Ids.
Scroll to the bottom of the list and add
mdx (or the language that isn't working for you).
Or in your JSON user or workspace settings, adjust the value of
cSpell.enabledLanguageIds to include the language causing the issue.
Note that if you do this, you'll want to include all the other languages you want targeted. Using this setting overrides all the defaults.