After updating to WordPress 5.0 I can't use the WPBakery Page Builder?
WordPress 5.0 introduced a new page editor called Gutenberg. Please ensure you have updated to the latest version of the theme and WPBakery Page Builder. To do this refer to your theme documentation.
Once you've done this you should see a blue WPBakery Page Builder button at the very top of your page. Clicking this disables the Gutenberg editor for this page so you can use the WPB page builder.
You can disable the Gutenberg editor permanently from WPBakery Page Builder > General Settings > Disable Gutenberg Editor.