jmuppala@: if you see this again would you mind sharing a copy of the /var/log/net.log and /var/log/messages files from the device that is experiencing the error?

sure

Looks like this bug was caused by this sequence of errors from the logs:

2018-07-25T15:35:34.897737-07:00 NOTICE dhcpcd[28780]: dhcpcd is running with reduced privileges
2018-07-25T15:35:34.904604-07:00 INFO dhcpcd[28780]: status changed to Init
2018-07-25T15:35:35.136977-07:00 ERR wpa_supplicant[632]: Could not set interface wlan0 flags (UP): Input/output error
2018-07-25T15:35:35.137010-07:00 ERR wpa_supplicant[632]: nl80211: Could not set interface 'wlan0' UP
2018-07-25T15:35:35.137033-07:00 NOTICE wpa_supplicant[632]: nl80211: deinit ifname=wlan0 disabled_11b_rates=0
2018-07-25T15:35:35.137362-07:00 ERR wpa_supplicant[632]: wlan0: Failed to initialize driver interface
2018-07-25T15:35:35.138134-07:00 ERR shill[28777]: [ERROR:object_proxy.cc(582)] Failed to call method: fi.w1.wpa_supplicant1.CreateInterface: object_path= /fi/w1/wpa_supplicant1: fi.w1.wpa_supplicant1.UnknownError: wpa_supplicant couldn't grab this interface.
2018-07-25T15:35:35.138188-07:00 ERR shill[28777]: [ERROR:dbus_method_invoker.h(112)] CallMethodAndBlockWithTimeout(...): Domain=dbus, Code=fi.w1.wpa_supplicant1.UnknownError, Message=wpa_supplicant couldn't grab this interface.
2018-07-25T15:35:35.138243-07:00 ERR shill[28777]: [ERROR:chromeos_supplicant_process_proxy.cc(130)] Failed to create interface: fi.w1.wpa_supplicant1.UnknownError wpa_supplicant couldn't grab this interface.
2018-07-25T15:35:35.139186-07:00 ERR shill[28777]: [ERROR:object_proxy.cc(582)] Failed to call method: fi.w1.wpa_supplicant1.GetInterface: object_path= /fi/w1/wpa_supplicant1: fi.w1.wpa_supplicant1.InterfaceUnknown: wpa_supplicant knows nothing about this interface.
2018-07-25T15:35:35.139236-07:00 ERR shill[28777]: [ERROR:dbus_method_invoker.h(112)] CallMethodAndBlockWithTimeout(...): Domain=dbus, Code=fi.w1.wpa_supplicant1.InterfaceUnknown, Message=wpa_supplicant knows nothing about this interface.
2018-07-25T15:35:35.140401-07:00 CRIT shill[28777]: [FATAL:chromeos_supplicant_process_proxy.cc(168)] Failed to get interface wlan0: fi.w1.wpa_supplicant1.InterfaceUnknown wpa_supplicant knows nothing about this interface.#012/usr/lib64/libbase-core-395517.so(_ZN4base5debug10StackTraceC1Ev+0x13) [0x7c9aa91dbb13]#012
2018-07-25T15:35:35.203485-07:00 INFO dhcpcd[28780]: exiting because flimflamd has died
2018-07-25T15:35:35.203504-07:00 INFO dhcpcd[28780]: eth0: removing interface

The following revision refers to this bug:
  https://chromium.googlesource.com/aosp/platform/system/connectivity/shill/+/1709b45b60b9ea26114ba9643b0a22a5876c3ff6

commit 1709b45b60b9ea26114ba9643b0a22a5876c3ff6
Author: Micah Morton <mortonm@chromium.org>
Date: Tue Jul 31 23:37:25 2018

shill_login_user: Ensure shill user profile dir is owned by shill:shill

We need to chown this dir to be owned by shill:shill even if it already
exists, so that when we update CrOS devices to running shill as
shill:shill (instead of root:root), the dir gets updated to the correct
permissions.

BUG=chromium:867171, chromium:867685 , chromium:865184 , chromium:867680 , chromium:864874 , chromium:865789 , chromium:866041 , chromium:866559 , chromium:866961 
TEST=flash 10820 image to lulu device. log in as user. configure VPN
stuff. flash new 10888 image to lulu and update shill_login_user script.
login and notice that these problems go away.

Change-Id: Ib487d3a36a7b351887e5c101f1e797a0ab21c3b9
Reviewed-on: https://chromium-review.googlesource.com/1153841
Commit-Ready: Micah Morton <mortonm@chromium.org>
Tested-by: Micah Morton <mortonm@chromium.org>
Reviewed-by: Abhishek Bhardwaj <abhishekbh@chromium.org>
Reviewed-by: Micah Morton <mortonm@chromium.org>

[modify] https://crrev.com/1709b45b60b9ea26114ba9643b0a22a5876c3ff6/bin/shill_login_user

Not able to reproduce this issue on 10928.0.0 (Babymega/Coral), hence closing the bug. Will re-open this bug if the issue pops up again.