Noticed the plugin is breaking quite badly in 3.1. I got this error when trying to create or edit discussions that expect calendar dates:
Follow-up: I am seeing this in the Reactions plugin too, I think it may be less to do with the plugin and more to do with MySQL. Investigation continues.
I can see in a number of places that dates are passed to MySQL like this:
'DateInserted' => date(DATE_ISO8601)
This will return a long-form ISO8601-compliant date string, like this:
However, MySQL does not accept ISO8601 date strings. It accepts almost-8601, YYYY-MM-DD HH:MM:SS
Okay I am flip-flopping - I do think there is a bug in this plugin that needs to be addressed (same with Yaga application).
But what I said in the previous comment is incorrect, as EventCalendar doesn't do dates like that. I'm not sure how it works, it appears to be Vanilla magic. I did fix Yaga along the way though, I should put a PR up for that.
ANOTHER UPDATE: I played myself, a bit. I had recently upgraded MySQL and it re-enabled strict mode.
HOWEVER, it seems dates are not being persisted. I can see them in the form post data, but they are not being saved. Hmm!