Simply said, It’s a sign that you have ALTERNATE_WP_CRON defined in your wp-config.php
In order to do some background processing (like publishing scheduled posts), WordPress redirects you to the URL with ?doing_wp_cron appended.
This is usually triggered by backup plugins such as UpDraft backups or All-In-One WP Migration.
If you want to disable this, simply open your wp-config.php file and delete the line containing ALTERNATE_WP_CRON
Another way to hide this is by managing redirection in the .htaccess file.
<IfModule mod_rewrite.c>
Options +FollowSymLinks
RewriteEngine On
RewriteCond %{QUERY_STRING} (^|&)doing_wp_cron= [NC]
RewriteRule (.*) /$1? [R=301,L]
</IfModule>
This can also be triggered because of an alternate cron job. To work around this, if you have access, you can enable an actual cron process (if your hosting will let you) and disable ALTERNATE_WP_CRON in your wp-config.php.
Hope this will help!