admin-ajax.php 400

I seem to get 400 for admin-ajax.php when I load my site.
POST https://xxx.com/wp-admin/admin-ajax.php?1588826892879 400 (Bad Request)

I have isolated the WPComplete plugin on the 2020 theme (no other plugins) and still see this.

Despite seeing this error, I do not see any issue with functionality.

Any ideas what might be going on?