Network port of RPi3 just goes dead (armv7l kernel)

[graysky]

For no reason that I can determine, my RPi3 experiences network failures at random times. Symptoms include no lights on the onboard LAN (no yellow and no green). The only way to recover is a manual power cycle. I found a similar report from another user experiencing. That user is not using a bridge network, he is using a simple DHCP profile so that makes me think the bridge in my setup is not to blame.

Details:
Distro: Arch ARM (armv7l not aarch64)
Hardware: RPi3
What's connected, truly headless: only power and LAN. No HDMI, no USB devices.
How the LAN is managed: systemd-networkd with bridge using the below settings.
Key software versions:

• linux-raspberrypi 4.9.39-1
• raspberrypi-bootloader 20170721-1
• raspberrypi-bootloader-x 20170721-1
• raspberrypi-firmware 20170721-1
• systemd 233.75-3.1

$this->bbcode_second_pass_code('', '/etc/systemd/network/br0.netdev
[NetDev]
Name=br0
Kind=bridge')

$this->bbcode_second_pass_code('', '/etc/systemd/network/br0.network
[Match]
Name=br0

[Network]
DHCP=ipv4')

$this->bbcode_second_pass_code('', '/etc/systemd/network/primary.network
[Match]
Name=eth0

[Network]
Bridge=br0
')

[graysky]

It seems that if I downgrade packages to the set from July 10th, it seems stable. When I update to current, the problem manifests but it's seemingly random. Some times, I have uptime for 2-3 days and other times, 10-15 min. I'd say that it was hardware, but the fact that the downgrade seems to prevent it is inconsistent with that. Here is a list of packages that are suspect:
$this->bbcode_second_pass_code('', 'grep downgrade /var/log/pacman.log | awk '{print $5 $6 $7 $8}'
bison(3.0.4-3->3.0.4-2)
zlib(1:1.2.11-2->1:1.2.11-1)
cpupower(4.12-1->4.11-2)
curl(7.54.1-2->7.54.1-1)
dnssec-anchors(20170711-1->20170228-1)
expat(2.2.2-1->2.2.1-1)
elinks(0.13-19->0.13-18)
haveged(1.9.1-3->1.9.1-2)
libelf(0.169-2->0.169-1)
iproute2(4.12.0-2->4.12.0-1)
libarchive(3.3.2-1->3.3.1-5)
pcre(8.41-1->8.40-1)
popt(1.16-9->1.16-8)
linux-raspberrypi(4.9.39-1->4.9.36-1)
pacman(5.0.2-2->5.0.2-1)
python(3.6.2-1->3.6.1-1)
python2(2.7.13-4->2.7.13-3)
raspberrypi-bootloader(20170721-1->20170703-1)
raspberrypi-bootloader-x(20170721-1->20170703-1)
raspberrypi-firmware(20170721-1->20170613-1)
s-nail(14.9.0-1->14.8.16-2)
vim-runtime(8.0.0722-1->8.0.0628-1)
vim(8.0.0722-1->8.0.0628-1)
')