ping tries to contact destination. Try nslookup as an alternative, see below.
I then logged into the Fritzbox (linux6 was switched off). I removed the unused connection for linux6 (even though it had the right address). I then switched on linux6 and it received the same address again.I pinged linux6 again and it worked.
FRITZ!Boxes work best with static host names and DHCP:
**i3-4130:~ #** hostnamectl
** Static hostname: i3-4130 **
Icon name: computer-desktop
Chassis: desktop
Machine ID: b650d066970b487eaffea649babf596a
Boot ID: 326bc295784c4a2a8384ad30ec38e305
Operating System: openSUSE Tumbleweed
CPE OS Name: cpe:/o:opensuse:tumbleweed:20210825
Kernel: Linux 5.13.12-2-default
Architecture: x86-64
Hardware Vendor: To Be Filled By O.E.M.
Hardware Model: To Be Filled By O.E.M.
**i3-4130:~ #**
On boot host i3-4130 advertises its name and asks the FRITZ!Box for an address.
**i3-4130:~ #** nslookup i3-4130
Server: 192.168.178.1
Address: 192.168.178.1#53
Name: i3-4130.fritz.box
Address: 192.168.178.29
Name: i3-4130.fritz.box
Address: 2001:XX:XX:XX:XX:XX:XX:XX
**i3-4130:~ #**
i3-4130 uses a minimal configuration file:
**i3-4130:~ #** cat /etc/systemd/network/wlan.network
[Match]
Name=w*
[Network]
DHCP=yes
Domains=fritz.box
**i3-4130:~ #**