Had SEC up and running for the last couple of months after spending a lot of time on styling, etc. Was happy with it in the end.

Today, when upgrading Revolution Slider (v6.2.1 "26th February 2020"), having both SEC and Rev Slider activated causes a "There has been a critical error on your website. Please check your site admin email inbox for instructions," when attempting to access WP admin. 

The site continued to function, particularly Rev Slider, however SEC showed no event entries (eg blank calendars). 

Console errors are:

-Failed to load resource: the server responded with a status of 500 (Internal Server Error)

-Stachethemes Event Calendar encountered an error (error) during get_events ajax request

1. Object
   1. status: 500
   2. response: "

      There has been a critical error on your website.

      Learn" class="redactor-linkify-object">https://wordpress.org/support/article/debugging-in-wordpress/">Learn more about debugging in WordPress.

      "
   3. __proto__: Object

----------------------

So, while I was initially certain that SEC was to blame, I also got:

When seeking help with this issue, you may be asked for some of the following information:
WordPress version 5.3.2
Current plugin: Slider Revolution (version 6.2.1)
PHP version 7.1.33

Error Details
=============
An error of type E_ERROR was caused in line 472 of the file /home/ppjc5/public_html/wp-content/plugins/revslider/admin/revslider-admin.class.php. Error message: Uncaught Error: Cannot use object of type Closure as array in /home/ppjc5/public_html/wp-content/plugins/revslider/admin/revslider-admin.class.php:472
Stack trace:
#0 /home/ppjc5/public_html/wp-includes/class-wp-hook.php(288): RevSliderAdmin->merge_addon_notices('')
#1 /home/ppjc5/public_html/wp-includes/class-wp-hook.php(312): WP_Hook->apply_filters(NULL, Array)
#2 /home/ppjc5/public_html/wp-includes/plugin.php(478): WP_Hook->do_action(Array)
#3 /home/ppjc5/public_html/wp-admin/admin.php(170): do_action('admin_init')
#4 /home/ppjc5/public_html/wp-admin/index.php(10): require_once('/home/ppjc5/pub...')
#5 {main}
  thrown

----------------------------

Disabling Rev Slider fixed the issue. And the problem is likely Rev Slider alone. However, you should be aware of the apparent conflict.