BTCPay not working over IPv6
The BTCPay service is not accessible over IPv6. This caused Let's Encrypt to fail to renew HTTPS certificates in #41185 (closed).
As a workaround, I removed the IPv6 address from LDAP, which in turn removed it from DNS. This fixed the certificate renewal.
A bit of research suggests that our version of Docker, 20.10.5, carries a bug that prevents the Docker proxy from binding exposed ports to IPv6. The release notes for 20.10.6 indicate that the bug received a fix.
Since Debian bookworm
ships with Docker 20.10.24, a simple fix might simply be to upgrade the machine.