You have been observed that, sometime Metadata from your site removed from Google SERPs.? It doesn’t mean your site has been penalized exactly. Even your site is Indexed in search engine and not much effect traffic on the web. Sometimes it happens, Google allow viewing Metadata associated with site in SERPs in a certain ratio of pages reviews and total number pages added recently to your site.
There could be the main reason of rich snippets viewing in Google SERPs of being disappearing the Metadata associated with the site. Means the snippets (is a program) generated content on your can be penalized by the Google SERPs. This could be the factor of disappearing the Metadata of site.
In terms of removing or disappearing the Metadata from site but not affected traffic that indicates its important too what attract most visitors towards your site.
However Search Engine loves original and Metadata content on your site. Rich snippets content could be a factor of harm for site rank.
