That's because of changes made in  issue 644304 , which were made in assumption that DMServer will just ignore requests with unknown policy types - which is apparently no longer true.

I'm preparing CL with a quick fix that will disable the new functionality on the client side.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f14a5fdb16cda4b707b127d1c8cf62115a72f709

commit f14a5fdb16cda4b707b127d1c8cf62115a72f709
Author: emaxx <emaxx@chromium.org>
Date: Fri Nov 18 14:21:32 2016

Disable fetching of policy for login screen apps

This disables fetching of policies for login screen apps, which used the
new policy type "google/chromeos/signinextension", as DMServer started
to respond with errors to requests with unknown policy types.

BUG= 666720 , 644304 
TEST=manual (run chromeos=1 build with an enrolled profile, navigate to chrome://policy, press "Reload policies", check that OK is displayed for the device policy)

Review-Url: https://codereview.chromium.org/2513903003
Cr-Commit-Position: refs/heads/master@{#433190}

[modify] https://crrev.com/f14a5fdb16cda4b707b127d1c8cf62115a72f709/chrome/browser/chromeos/policy/device_cloud_policy_browsertest.cc
[modify] https://crrev.com/f14a5fdb16cda4b707b127d1c8cf62115a72f709/chrome/browser/chromeos/policy/device_cloud_policy_manager_chromeos.h

This should be fixed now.

Thiemo, thanks for triaging this!

And I'll request a merge once the fix is confirmed to work on ToT.

This fix is required for enrolled enterprise devices.

Note that the fix disables some functionality (fetching of admin policies for Chrome OS login screen apps), but this was anyway not expected to be fully functional in M56.

Your change meets the bar and is auto-approved for M56 (branch: 2924)

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ee89d810be7379fc0c713cf4f806efe5c38a548d

commit ee89d810be7379fc0c713cf4f806efe5c38a548d
Author: Maksim Ivanov <emaxx@chromium.org>
Date: Fri Nov 18 17:50:09 2016

Disable fetching of policy for login screen apps

This disables fetching of policies for login screen apps, which used the
new policy type "google/chromeos/signinextension", as DMServer started
to respond with errors to requests with unknown policy types.

BUG= 666720 , 644304 
TEST=manual (run chromeos=1 build with an enrolled profile, navigate to chrome://policy, press "Reload policies", check that OK is displayed for the device policy)

Review-Url: https://codereview.chromium.org/2513903003
Cr-Commit-Position: refs/heads/master@{#433190}
(cherry picked from commit f14a5fdb16cda4b707b127d1c8cf62115a72f709)

Review URL: https://codereview.chromium.org/2518613002 .

Cr-Commit-Position: refs/branch-heads/2924@{#3}
Cr-Branched-From: 3a87aecc31cd1ffe751dd72c04e5a96a1fc8108a-refs/heads/master@{#433059}

[modify] https://crrev.com/ee89d810be7379fc0c713cf4f806efe5c38a548d/chrome/browser/chromeos/policy/device_cloud_policy_browsertest.cc
[modify] https://crrev.com/ee89d810be7379fc0c713cf4f806efe5c38a548d/chrome/browser/chromeos/policy/device_cloud_policy_manager_chromeos.h

Note that device policy issues usually don't warrant blocking the dev release.  (I've only learned that recently.)

https://docs.google.com/document/d/1SVFeHFp6bnpFA6LseShcAPXrAFRaOFjGVeUlx8oo7rk/edit

#c10, As you've mentioned, don't think this be added to the dev-blocker qual list. 
But this does block feature testing or Sanity testing efforts. So Pri:0 would be a good label to signify urgency. 

M	ChromeOS	Chrome	ARC	Type	Channel
56	9000.15.0	56.0.2924.12	3535779	release	dev


I have been testing Enterprise functionality using M56 builds (dev channel) since this Monday, Nov. 28 and doing a lot of auto update to different builds, unplug and plug Ethernet, power off and power on devices.  chrome://policy page is always reloaded timely with "Policy cache OK".

Issue 668329 has been merged into this issue.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5eb4901df37717dd05fd071a807a0ebaf563f0f3

commit 5eb4901df37717dd05fd071a807a0ebaf563f0f3
Author: emaxx <emaxx@chromium.org>
Date: Fri Dec 30 03:29:57 2016

Re-enable fetching component policies for login screen apps

This CL relands enabling fetching of policies for Chrome OS login screen
apps.

The originally landed code was temporarily disabled due to DMServer
responding with errors when an unknown policy type was requested. Now
this can be enabled back, after the DMServer got fixed to at least
ignore the new policy type (until it starts to actually provide policies
with this type).

BUG= 644304 , 666720 
TEST=re-enabled browser tests;
     manual test: sign into an enrolled device, go to chrome://policy
     and check that the device policies were fetched successfully

Review-Url: https://codereview.chromium.org/2603463003
Cr-Commit-Position: refs/heads/master@{#441015}

[modify] https://crrev.com/5eb4901df37717dd05fd071a807a0ebaf563f0f3/chrome/browser/chromeos/policy/device_cloud_policy_browsertest.cc
[modify] https://crrev.com/5eb4901df37717dd05fd071a807a0ebaf563f0f3/chrome/browser/chromeos/policy/device_cloud_policy_manager_chromeos.cc
[modify] https://crrev.com/5eb4901df37717dd05fd071a807a0ebaf563f0f3/chrome/browser/chromeos/policy/device_cloud_policy_manager_chromeos.h
[modify] https://crrev.com/5eb4901df37717dd05fd071a807a0ebaf563f0f3/chrome/browser/chromeos/policy/device_cloud_policy_manager_chromeos_unittest.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/3cce5ba611580090dbbd55686e0372a2a4955bbe

commit 3cce5ba611580090dbbd55686e0372a2a4955bbe
Author: tnagel <tnagel@chromium.org>
Date: Thu Jan 12 19:47:10 2017

Revert of Re-enable fetching component policies for login screen apps (patchset #3 id:40001 of https://codereview.chromium.org/2603463003/ )

Reason for revert:
I'm very sorry I have to revert this since it's breaking device policy updates.

https://bugs.chromium.org/p/chromium/issues/detail?id=679956#c7

Original issue's description:
> Re-enable fetching component policies for login screen apps
>
> This CL relands enabling fetching of policies for Chrome OS login screen
> apps.
>
> The originally landed code was temporarily disabled due to DMServer
> responding with errors when an unknown policy type was requested. Now
> this can be enabled back, after the DMServer got fixed to at least
> ignore the new policy type (until it starts to actually provide policies
> with this type).
>
> BUG= 644304 , 666720 
> TEST=re-enabled browser tests;
>      manual test: sign into an enrolled device, go to chrome://policy
>      and check that the device policies were fetched successfully
>
> Committed: https://crrev.com/5eb4901df37717dd05fd071a807a0ebaf563f0f3
> Cr-Commit-Position: refs/heads/master@{#441015}

TBR=emaxx@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG= 644304 , 666720 

Review-Url: https://codereview.chromium.org/2621413007
Cr-Commit-Position: refs/heads/master@{#443328}

[modify] https://crrev.com/3cce5ba611580090dbbd55686e0372a2a4955bbe/chrome/browser/chromeos/policy/device_cloud_policy_browsertest.cc
[modify] https://crrev.com/3cce5ba611580090dbbd55686e0372a2a4955bbe/chrome/browser/chromeos/policy/device_cloud_policy_manager_chromeos.cc
[modify] https://crrev.com/3cce5ba611580090dbbd55686e0372a2a4955bbe/chrome/browser/chromeos/policy/device_cloud_policy_manager_chromeos.h
[modify] https://crrev.com/3cce5ba611580090dbbd55686e0372a2a4955bbe/chrome/browser/chromeos/policy/device_cloud_policy_manager_chromeos_unittest.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/94c4e6b642d971a31680fbb19858f56e1a4d8d7b

commit 94c4e6b642d971a31680fbb19858f56e1a4d8d7b
Author: emaxx <emaxx@chromium.org>
Date: Thu Feb 09 00:19:32 2017

Reland Re-enable fetching component policies for login screen apps

This CL relands enabling fetching of policies for Chrome OS login screen
apps.

The originally landed code was temporarily disabled due to DMServer
responding with errors when an unknown policy type was requested. Now
this can be enabled back, after the DMServer got fixed to at least
ignore the new policy type (until it starts to actually provide policies
with this type).

TBR=tnagel@chromium.org

BUG= 644304 , 666720 
TEST=re-enabled browser tests;
     manual test: sign into an enrolled device, go to chrome://policy
     and check that the device policies were fetched successfully

Review-Url: https://codereview.chromium.org/2685893004
Cr-Commit-Position: refs/heads/master@{#449157}

[modify] https://crrev.com/94c4e6b642d971a31680fbb19858f56e1a4d8d7b/chrome/browser/chromeos/policy/device_cloud_policy_browsertest.cc
[modify] https://crrev.com/94c4e6b642d971a31680fbb19858f56e1a4d8d7b/chrome/browser/chromeos/policy/device_cloud_policy_manager_chromeos.cc
[modify] https://crrev.com/94c4e6b642d971a31680fbb19858f56e1a4d8d7b/chrome/browser/chromeos/policy/device_cloud_policy_manager_chromeos.h
[modify] https://crrev.com/94c4e6b642d971a31680fbb19858f56e1a4d8d7b/chrome/browser/chromeos/policy/device_cloud_policy_manager_chromeos_unittest.cc