The plugin is All In One Event Calendar by Time.ly. Maybe this link is useful:
I had several problems with conflicts between this (and another calendar plugin) with the theme I’m using which Aegaeus by HB-Themes. On advice from HB-Themes there is custom CSS in the theme options and a modified single-ai1ec-event.php module in a child theme.
I don’t have a great deal of experience at this: is there any possibility that a WordPress plugin update could trigger a problem elsewhere in the site configuration? By the way, it was only the Connections 8.3.1 plugin that was updated.
I’m not convinced of the stability of the overall site following the update and I wonder if it wouldn’t be best to restore the home directory and sql database (I have back from immediately before the plugin update), see if it’s a stable working solution and then try the Connections plugin update again.
Let me know what you think.