When using search google console on an Ametys website we can check that hcalendar microformats are used (http://microformats.org/wiki/hCalendar) but the class vevent is showed in the content digests using Link and Abstract.
This is generating a lot of errors because some informations are missing (for example location tag).
My suggestion is to use the h-event (http://microformats.org/wiki/h-event), but only on full news and not on content digests that does not contains all the required informations that cause some problems for Google.
For example, in news-abstract:

<xsl:variable name="common-content-css-class-name">news view-abstract<xsl:variable>

Same in news-link