By default, vim spell checker is code aware, so it doesn't spell-check code parts of the file. In effect, in markdown it considers (pandoc multiline) tables to be codes and thus doesn't spell-check their contents.
Is it possible to override this? Or enable spell-check for the entire file including code.
As far as I'm able to determine, there is no way to tell Vim to ignore the spellcheck suggestions in the syntax file and to just "check everything".
A fairly heavy-handed workaround is to disable syntax entirely with :syn off;
you can re-enable this with :syn on.
Specifically for Markdown, you can disable highlighting of code blocks with
:syn clear markdownCodeBlock; you can reset this with :syn on as well.