Local DNS dosnet work as expected / Wrong Names in GUI

[Just2Confuse]

Hi,
I have changed my router, now AVM/6690 Cable. My local clients are actually largely clean.

For example: FireTV = 192.168.1.44

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root@DietPi:~# nslookup 192.168.1.44
44.1.168.192.in-addr.arpa       name = FireTV.fritz.box.
44.1.168.192.in-addr.arpa       name = Android.fritz.box.
44.1.168.192.in-addr.arpa       name = amazon-d97e3ab28.fritz.box.

root@DietPi:~# cat /etc/resolv.conf
nameserver 192.168.1.1
root@DietPi:~#
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AdGuard shows amazon-d97e3ab28.fritz.box. PiHole select FireTV.fritz.box with the same 3 adresses at nslookup. 
Im not sure why i get 3 answers, other clients working with one answer, some with two (but the right pick at the name)
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root@DietPi:~# nslookup 192.168.1.31
31.1.168.192.in-addr.arpa       name = Hue-Station.fritz.box.
31.1.168.192.in-addr.arpa       name = 0017887b0b09.fritz.box.

root@DietPi:~# nslookup 192.168.1.30
30.1.168.192.in-addr.arpa       name = Diskstation.fritz.box.

root@DietPi:~#
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AVM Setup Picture -> https://i.postimg.cc/8kL8QYhg/firetv.png

Regards

[Just2Confuse]

Hmmm, OK. It looks like the name like this are coming from the devices itself. But im not sure why AdGuard Home is pikcing the names from the bottom while pihole is tacking the name from the Router.