Thank you for clarifying this!
This is good news because as long as those errors only come up in the Google Webmaster tools, there is no actual technical error here. The reporting of those soft 404s is just Google’s Webmaster tools saying – “hey, you might want to make sure these 404s are actually 404s.”
And in the context of The Events Calendar, they are 404s.
So reporting them as 404s is the correct thing to do here. I know how alarming it can be to see a bunch of notices in the Webmaster tools, but that is just diagnostic information and the soft 404s are actually a good thing, especially when SEO is a priority.
To read more about this, check out our knowledgebase article here on the topic: https://theeventscalendar.com/knowledgebase/404_and_seo/
That explains a bit more about what these 404s are, and how search engines handle them.
I hope this helps!