Comment # 4 on bug 1188019 from Ivan Ivanov

Hm, my RPi4 start getting sluggish. For me wickedd-dhcp6 was 
the offending process. I have changed BOOTPROTO to dhcp4, 
i.e. IPv4 only and performance is back.

# journalctl -u wickedd-dhcp6 --since=today | head
-- Journal begins at Mon 2021-06-28 00:00:00 UTC, ends at Fri 2021-07-23
06:57:16 UTC. --
Jul 23 00:00:00 localhost wickedd-dhcp6[546]: eth0: ignoring REPLY message xid
0x6750c4 in state SELECTING from fe80::dea6:32ff:fe3c:1825: rapid-commit lease
without usable address
Jul 23 00:00:00 localhost wickedd-dhcp6[546]: eth0: ignoring REPLY message xid
0x6750c4 in state SELECTING from fe80::dea6:32ff:fe3c:1825: rapid-commit lease
without usable address
Jul 23 00:00:00 localhost wickedd-dhcp6[546]: eth0: ignoring REPLY message xid
0x6750c4 in state SELECTING from fe80::dea6:32ff:fe3c:1825: rapid-commit lease
without usable address