Had this weird problem witch seems to have solved itself.
After the update and a reboot the network was not working.
Checked, cables, swithes, dhcp server, other machines on the network.
Rebooted again, the ip configuration was not being set.
One failed service using (systemctl list-units --state=failed) the wait on network service witch seems to be expected with no connection.
Recreated the wired network configuration, with static, no network connection. (machine not reachable from other machines.
Reverted to a older kernel(5.7), still same issue.
Recreated wired network again, with dhcp defaults, no network, suspect hardware failure on the motherboard. Rebooted into an old windows10 installation, network was working so no hardware problem.
Rebooted to latest stable (5.8) kernel and network works again.
Source of the problem unknown, i found the lines below in the pacman update log, but after searching a bit is does not seems to be the cause of the problem.
[2020-08-28T21:12:14+0200] [ALPM] running ‘30-systemd-sysctl.hook’…
[2020-08-28T21:12:14+0200] [ALPM-SCRIPTLET] Not setting net/ipv4/conf/all/rp_filter (explicit setting exists).
[2020-08-28T21:12:14+0200] [ALPM-SCRIPTLET] Not setting net/ipv4/conf/default/rp_filter (explicit setting exists).
[2020-08-28T21:12:14+0200] [ALPM-SCRIPTLET] Not setting net/ipv4/conf/all/accept_source_route (explicit setting exists).
[2020-08-28T21:12:14+0200] [ALPM-SCRIPTLET] Not setting net/ipv4/conf/default/accept_source_route (explicit setting exists).
[2020-08-28T21:12:14+0200] [ALPM-SCRIPTLET] Not setting net/ipv4/conf/all/promote_secondaries (explicit setting exists).
[2020-08-28T21:12:14+0200] [ALPM-SCRIPTLET] Not setting net/ipv4/conf/default/promote_secondaries (explicit setting exists).
[2020-08-28T21:12:14+0200] [ALPM] running ‘30-systemd-tmpfiles.hook’…`
There are some errors in the systemd logs (journalctl -k -p err -b -# where # is the reboot count) for the previous boots where there was no network.
aug 28 22:42:22 XX kernel: r8169 0000:03:00.0 enp3s0: rtl_rxtx_empty_cond == 0 (loop: 42, delay: 100).
aug 28 22:42:32 XX kernel: r8169 0000:03:00.0 enp3s0: rtl_rxtx_empty_cond == 0 (loop: 42, delay: 100).
These errors are not there in the last boot when the network came up.
Problem solved I hope 