I added a second language (Dutch) to the first language (English), which made all manufacturers dissappear. No problems with products and categories. (J1.7.2 stable, VM2.0.2 stable)
Try to switch the language in FE, because the language reflect always your Joomla front-end settings.
If you changed the default FE language and never set the manufacturers in the default lang this are simply not found and not displayed.