Google has had enough of people using the event markup in a misleading way and is now sending out a strict warning that if you use this markup in any other way then its intended purpose, Google may go ahead and penalize your site. The penalty will be in the form of a manual action which would result in your site not being able to show any rich snippets in the Google search results.
This is the same thing as the spammy structured markup manual actions and Google has not been shy with them in the past. But here you have Google (1) updating the events schema guidelines and (2) telling people not to use them in the “coupons/vouchers space” or other manners that it is not meant for.
In short, many in the coupons/vouchers space have been using them to markup their coupons in the rich results. Google said “as much as using a discount voucher can be a very special thing, that doesnât make coupons or vouchers events or ‘saleEvents’.” “Using Event markup to describe something that is not an event creates a bad user experience, by triggering a rich result for something that will happen at a particular time, despite no actual event being present,” Google added.
Here is a spammy rich snippet for event schema in this space:
Since this creates a misleading user experience, we may take manual action on such cases. In case your website is affected by such a manual action, you will find a notification in your Search Console account. If a manual action is taken, it can result in structured data markup for the whole site not being used for search results.
I suspect there might be an increase in spammy structured markup manual actions in the near future.
Forum discussion at Twitter.