Hi again!
Have a DHCPv4 server on an interface with static ARP enabled and reserved IPs for MACs defined.
A Grundig DTR5000 2.0 does not play nice with this setup, it does a DHCP discover about every 60 seconds
2020-08-08T12:02:35 dhcpd[15751]: DHCPACK on 10.0.2.5 to 30:58:90:aa:bb:cc via igb2
2020-08-08T12:02:35 dhcpd[15751]: DHCPREQUEST for 10.0.2.5 (10.0.2.1) from 30:58:90:aa:bb:cc via igb2
2020-08-08T12:02:35 dhcpd[15751]: DHCPOFFER on 10.0.2.5 to 30:58:90:aa:bb:cc via igb2
2020-08-08T12:02:35 dhcpd[15751]: DHCPDISCOVER from 30:58:90:aa:bb:cc via igb2
2020-08-08T12:01:58 dhcpd[15751]: DHCPACK on 10.0.2.5 to 30:58:90:aa:bb:cc via igb2
2020-08-08T12:01:58 dhcpd[15751]: DHCPREQUEST for 10.0.2.5 (10.0.2.1) from 30:58:90:aa:bb:cc via igb2
2020-08-08T12:01:58 dhcpd[15751]: DHCPOFFER on 10.0.2.5 to 30:58:90:aa:bb:cc via igb2
2020-08-08T12:01:58 dhcpd[15751]: DHCPDISCOVER from 30:58:90:aa:bb:cc via igb2
2020-08-08T12:00:51 dhcpd[15751]: DHCPACK on 10.0.2.5 to 30:58:90:aa:bb:cc via igb2
2020-08-08T12:00:51 dhcpd[15751]: DHCPREQUEST for 10.0.2.5 (10.0.2.1) from 30:58:90:aa:bb:cc via igb2
2020-08-08T12:00:51 dhcpd[15751]: DHCPOFFER on 10.0.2.5 to 30:58:90:aa:bb:cc via igb2
2020-08-08T12:00:51 dhcpd[15751]: DHCPDISCOVER from 30:58:90:aa:bb:cc via igb2
2020-08-08T11:56:59 dhcpd[15751]: DHCPACK on 10.0.2.5 to 30:58:90:aa:bb:cc via igb2
2020-08-08T11:56:59 dhcpd[15751]: DHCPREQUEST for 10.0.2.5 (10.0.2.1) from 30:58:90:aa:bb:cc via igb2
2020-08-08T11:56:59 dhcpd[15751]: DHCPOFFER on 10.0.2.5 to 30:58:90:aa:bb:cc via igb2
2020-08-08T11:56:59 dhcpd[15751]: DHCPDISCOVER from 30:58:90:aa:bb:cc via igb2
2020-08-08T11:55:52 dhcpd[15751]: DHCPACK on 10.0.2.5 to 30:58:90:aa:bb:cc via igb2
2020-08-08T11:55:52 dhcpd[15751]: DHCPREQUEST for 10.0.2.5 (10.0.2.1) from 30:58:90:aa:bb:cc via igb2
2020-08-08T11:55:52 dhcpd[15751]: DHCPOFFER on 10.0.2.5 to 30:58:90:aa:bb:cc via igb2
2020-08-08T11:55:52 dhcpd[15751]: DHCPDISCOVER from 30:58:90:aa:bb:cc via igb2
2020-08-08T11:54:56 dhcpd[15751]: DHCPACK on 10.0.2.5 to 30:58:90:aa:bb:cc via igb2
2020-08-08T11:54:56 dhcpd[15751]: DHCPREQUEST for 10.0.2.5 (10.0.2.1) from 30:58:90:aa:bb:cc via igb2
2020-08-08T11:54:52 dhcpd[15751]: DHCPOFFER on 10.0.2.5 to 30:58:90:aa:bb:cc via igb2
2020-08-08T11:54:52 dhcpd[15751]: DHCPDISCOVER from 30:58:90:aa:bb:cc via igb2
2020-08-08T11:54:23 dhcpd[15751]: DHCPACK on 10.0.2.5 to 30:58:90:aa:bb:cc via igb2
2020-08-08T11:54:23 dhcpd[15751]: DHCPREQUEST for 10.0.2.5 (10.0.2.1) from 30:58:90:aa:bb:cc via igb2
2020-08-08T11:54:23 dhcpd[15751]: DHCPOFFER on 10.0.2.5 to 30:58:90:aa:bb:cc via igb2
2020-08-08T11:54:23 dhcpd[15751]: DHCPDISCOVER from 30:58:90:aa:bb:cc via igb2
2020-08-08T11:53:12 dhcpd[15751]: DHCPACK on 10.0.2.5 to 30:58:90:aa:bb:cc via igb2
2020-08-08T11:53:12 dhcpd[15751]: DHCPREQUEST for 10.0.2.5 (10.0.2.1) from 30:58:90:aa:bb:cc via igb2
2020-08-08T11:53:09 dhcpd[15751]: DHCPACK on 10.0.2.5 to 30:58:90:aa:bb:cc via igb2
2020-08-08T11:53:09 dhcpd[15751]: DHCPREQUEST for 10.0.2.5 (10.0.2.1) from 30:58:90:aa:bb:cc via igb2
2020-08-08T11:53:09 dhcpd[15751]: DHCPOFFER on 10.0.2.5 to 30:58:90:aa:bb:cc via igb2
2020-08-08T11:53:09 dhcpd[15751]: DHCPDISCOVER from 30:58:90:aa:bb:cc via igb2
and often looses contact to wifi AP (a raspi 1 with wifi adapter in bridge mode on raspbian buster, no DHCP).
No updates available for the Grundig.
Any ideas how to debug this? :-)
...a "major relocation" of the wifi AP apparently resolved the issue for the moment... ;-)