vim folding messes up syntax highlighting

• Ctrl+L in normal mode forces a redraw and often fixes syntax colour problems.
• zRzMzx (i.e., expand all folds, contract all folds, fold to show current line) sometimes fixes syntax highlighting problems related to folds

I don't edit LaTeX, but perhaps you want ":syn sync fromstart"? Just be warned that this can significantly slow down Vim since it forces Vim to do syntax highlighting parsing for the whole file rather than a section of the file. See ::help :syn-sync".