Using the per-revision bisect providing the bisect results,
Good build: 55.0.2879.0(Revision:422347).
Bad build: 55.0.2880.0 (Revision:422654).

You are probably looking for a change made after 422652 (known good), but no later than 422653 (first known bad).

CHANGELOG URL:

The script might not always return single CL as suspect as some perf builds might get missing due to failure.
 
https://chromium.googlesource.com/chromium/src/+log/3bddafc6834c9487e6223168120f5de7ecbf1d2b..38d6995aaeade8b5cc6df9d1c7d3fb9cf6be176e

Review URL : https://codereview.chromium.org/2386533002

From the CL above, assigning the issue to the concern owner 

@dbeam - Could you please check whether this is caused with respect to your change, if not please help us in assigning it to the right owner.


Thanks!

Adding RB label as this is a recent regression

are there script errors in the console when this happens?

With response to comment #3, there are no script errors in the console.
Please refer the attached screenshot.
Thanks.

Deleted: Actual_screenshot.jpg 113 KB

	Actual_screenshot.jpg 113 KB View Download

dbeam@, could you please take a look and fix this issue as this is marked as M55 stable blocker.
thank you

Gentle Ping! Can we get any update on this issue as per comment #4

I've dug fairly deeply into this one

splices added outside of the range of iron-list's _virtualStart / _virtualEnd aren't being handled correctly

so if the user scrolls down and a new download is started at the top (which is generally how the UI works), there can be issues

ffu@/egarciad@: ideas?

This PR should fix the issue: https://github.com/PolymerElements/iron-list/pull/339

**** Bulk edit -  please ignore if not applicable ****

A friendly reminder that M55 Stable is launch is coming soon! Your bug is labelled as Stable ReleaseBlock, pls make sure to land the fix and get it merged into the release branch ASAP so it gets enough baking time in Beta (before Stable promotion). Thank you!

i don't think this is a "really needs a merge" change

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9ce83c55f556e739b053e6be5f0034870be47c37

commit 9ce83c55f556e739b053e6be5f0034870be47c37
Author: dbeam <dbeam@chromium.org>
Date: Wed Oct 26 23:55:02 2016

MD Downloads: handle date hiding/showing more sanely

Previously, items where created by accessing the physical DOM. As in:
someElementItem.hideDate = true/false. But then hideDate was moved to
an item's data. I accidentally left a property binding around.
Additionally, changing .data.hideDate doesn't actually trigger observers
in iron-list to fire as it's changing a sub-property of a complex
object. So instead, use the .set() API to ensure iron-list is notified
so it can update the template instance's data for the physical itmes it
owns.

It may be possible to test this, but:
* we've had issues in the past testing multiple items in an iron-list
  (and this test would require at least 2 items to be useful)
* you're not really supposed to use or depend on the physical items
  of an iron-list, which is actually what we'd need to check

R=dpapad@chromium.org
BUG= 656580 
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2449853006
Cr-Commit-Position: refs/heads/master@{#427883}

[modify] https://crrev.com/9ce83c55f556e739b053e6be5f0034870be47c37/chrome/browser/resources/md_downloads/crisper.js
[modify] https://crrev.com/9ce83c55f556e739b053e6be5f0034870be47c37/chrome/browser/resources/md_downloads/manager.html
[modify] https://crrev.com/9ce83c55f556e739b053e6be5f0034870be47c37/chrome/browser/resources/md_downloads/manager.js
[modify] https://crrev.com/9ce83c55f556e739b053e6be5f0034870be47c37/chrome/browser/resources/md_downloads/vulcanized.html
[modify] https://crrev.com/9ce83c55f556e739b053e6be5f0034870be47c37/chrome/browser/resources/md_history/app.crisper.js

Tested the issue on Windows, Mac and Linux using Chrome# 56.0.2902.0 and is still reproducible. 
Attaching screen cast of the issue for further reference.
Thank You.

Deleted: 656580.mov 3.4 MB

656580.mov 3.4 MB Download

Forgot to update the revision of the Chrome Version:
56.0.2902.0 (Official Build) dev (64-bit)
Revision 22203b32bdae9236d23cc89e70772721315f2d1f-refs/heads/master@{#427892}

Thank You.

msrchandra@: yeah, that's not surprising.  there's another fix in the pipeline:
https://codereview.chromium.org/2468963003

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/bb6e013c7fbe3add00dc47433357ebb43c81a693

commit bb6e013c7fbe3add00dc47433357ebb43c81a693
Author: dbeam <dbeam@chromium.org>
Date: Tue Nov 01 20:56:22 2016

MD Downloads: pick up iron-list PR to fix unassigned model (stacking)

R=dpapad@chromium.org
BUG= 656580 
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2468963003
Cr-Commit-Position: refs/heads/master@{#429103}

[modify] https://crrev.com/bb6e013c7fbe3add00dc47433357ebb43c81a693/chrome/browser/resources/md_downloads/crisper.js
[modify] https://crrev.com/bb6e013c7fbe3add00dc47433357ebb43c81a693/chrome/browser/resources/md_history/app.crisper.js
[modify] https://crrev.com/bb6e013c7fbe3add00dc47433357ebb43c81a693/third_party/polymer/v1_0/bower.json
[modify] https://crrev.com/bb6e013c7fbe3add00dc47433357ebb43c81a693/third_party/polymer/v1_0/components-chromium/iron-list/bower.json
[modify] https://crrev.com/bb6e013c7fbe3add00dc47433357ebb43c81a693/third_party/polymer/v1_0/components-chromium/iron-list/iron-list-extracted.js
[modify] https://crrev.com/bb6e013c7fbe3add00dc47433357ebb43c81a693/third_party/polymer/v1_0/components_summary.txt