Actually, we had a user report a similar issue and they worked with us to identify the issue.
The webshop is connected through cloudflare and some DNS records (AAAA) were not present. This caused the reading through the revert server. Since I updated these records, the notification is gone.
It is possible your issue was related to the same missing AAAA records and invalid DNS configuration.
I hope this helps others that may come across this.
The support topic is here:
https://www.ads-software.com/support/topic/source-for-blacklist/page/2/#post-15937755