Automatic cache purge API errors

Every time I save a post the plugin attempts to purge the Cloudflare cache (as intended) but logs an error in the PHP log:

2020/06/13 15:20:05 [error] 121024#121024: *2058760 FastCGI sent in stderr: "PHP message: [Cloudflare] ERROR: [CLIENT API] Array
(
[type] => response
[body] => Array
(
[result] =>
[success] =>
[errors] => Array
(
[0] => Array
(
[code] => 1084
[message] => Unable to purge , which is an invalid URL.
)
[1] => Array
(
[code] => 1016
[message] => One or more cache purge errors
)
)
[messages] => Array
(
)
)
)" while reading response header from upstream, client: 90.255.184.151, server: www.mysite.com, request: "POST /wp-admin/post.php?post=25331&action=edit&meta-box-loader=1&meta-box-loader-nonce=bea5f1ef28&_locale=user HTTP/1.0", upstream: "fastcgi://unix:/var/run/php7.4-fpm-mysite.sock:", host: "www.mysite.com", referrer: "https://www.mysite.com/wp-admin/post.php?post=25331&action=edit"

It looks like it is sending an empty URL to the purge API.

I've taken a cursory look at the code and followed it through to getPostRelatedLinks but not digged deeper. Any ideas on this? Is it a known issue?