I can't ping6 my domains in my home network: "mydomain.tld: Name or service not known"

Setup

Desktop computer (MyComputer)
- Mobo: ASRock
- Distro: Arch Linux
Yunohost Server (Yunohost)
- Mobo: Raspberry Pi 3
- Distro: Debian
- Main App: Yunohost/NextCloud
- Domain registered at godaddy.com (mydomain.tld)
Yunohost Server (Xroklaus)
- Mobo: Raspberry Pi 3
- Distro: Debian
- Main App: Yunohost/Duniter
- Domain registered at FreeDNS.afraid.org (mydomain2.tld)
Modem
- Fritz!Box 7581

I have trouble pinging my domains on ipv6.

[me@MyComputer ~]$ ping -4 mydomain.tld -c 3
PING mydomain.tld (my.ip.v.4) 56(84) bytes of data.
64 bytes from my.isp.ad.dr (my.ip.v.4): icmp_seq=1 ttl=63 time=2.56 ms
64 bytes from my.isp.ad.dr (my.ip.v.4): icmp_seq=2 ttl=63 time=2.74 ms
64 bytes from my.isp.ad.dr (my.ip.v.4): icmp_seq=3 ttl=63 time=2.50 ms

--- mydomain.tld ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2003ms
rtt min/avg/max/mdev = 2.504/2.605/2.743/0.101 ms
[me@MyComputer ~]$ ping -6 mydomain.tld -c 3
mydomain.tld: Name or service not known
[me@MyComputer ~]$ ping -6 mydomain2.tld -c 3
mydomain2.tld: Name or service not known
[me@MyComputer ~]$ ping -6 ipv6.google.com -c 3
PING ipv6.google.com(ham02s17-in-x0e.1e100.net (2a00:1450:4005:80b::200e))    56 data bytes
64 bytes from ham02s17-in-x0e.1e100.net (2a00:1450:4005:80b::200e): icmp_seq=1 ttl=54 time=16.5 ms
64 bytes from ham02s17-in-x0e.1e100.net (2a00:1450:4005:80b::200e): icmp_seq=2 ttl=54 time=16.5 ms
64 bytes from ham02s17-in-x0e.1e100.net (2a00:1450:4005:80b::200e): icmp_seq=3 ttl=54 time=16.3 ms

--- ipv6.google.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2002ms
rtt min/avg/max/mdev = 16.303/16.487/16.588/0.167 ms

Modem settings

Solution

It turns out that Fritz!Box suppresses DNS responses, which I need in order to test my home network. Sheesh. It took me two months to figure this out.