Why do I get this warning related to DNS packet sizes on Digital Ocean with IPv6?

At the moment, I have a DNS master being served from my Gandi VPS and slaves operated by friends at Linode. I just set up a new VPS to test as a slave at Digital Ocean, but when I run this DNSSEC test,

I get this warning for any queries directed to the IPv6 address of the Digital Ocean VPS:

No response was received until the UDP payload size was decreased,
indicating that the server might be attempting to send a payload that
exceeds the path maximum transmission unit (PMTU) size.
(2604:a880:2:d0::826:6001, UDP_0_EDNS0_32768_4096)

(This address “2604:a880:2:d0::826:6001” is for the IPv6 side of my D.O. VPS. This warning does not appear for any of the Linode or Gandi systems, which are using both IPv4 and IPv6.)

I do run a firewall (ufw), but I get the same warnings regardless of disabling or enabling the firewall.

Thank you, David

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Have you submitted a support ticket? When it comes to networking issues, your best bet would be to submit a ticket and let the support team address the issue on their end. Since this is a community, the best possible scenario is that one of the support team drops by or someone here knows how to fix a specific issue, but when it comes to actual issues that are limiting, I’d get in touch directly.

When it comes to software questions, or general how-to’s, the community is perfect, but for something that may require physical access to something those within the community are unable to access, that would be my recommendation.