In your calendar dashboard under Events > Import Feeds > Import Feeds tab >

You click on the Refresh button, but the feed never gives you a confirmation message that the sync/refresh operation completed.

Most likely, the reason could be that your host is reaching it’s PHP memory limit — and then the feed hangs.

I suggest increasing the memory limit, and try the feed refresh again — it should finish, then produce either a confirmation or an error message — this is how you know it finishes.

There are 4 ways to increase your PHP memory limit:

1. Add this to your wp-config file:

define(‘WP_MEMORY_LIMIT’, ‘256M’);

or

2. Edit your PHP.ini file (requires access to your server files).  If you have access to your PHP.ini file, change the line in PHP.ini
If your line shows 64M, try 256M:

memory_limit = 256M

or

3. Edit your .htaccess file.  If you don’t have access to PHP.ini try adding this to an .htaccess file:

php_value memory_limit 256M

4. Contact your Web Hosting Support

Ask your web host to increase the upload_max_filesize value for you to 256M