I think this should be assigned to Ben's team but I dont know what is the appropriate label/component.. 
Ting-Yuan was going to find out..

I'm seeing the same problem on chell; I.e., it also happens on amd64.

hctsai@ and cywang@ were looking at this yesterday.

After bisecting for the root cause, I found the score flipping commit is from Chrome:

commit d892f9592860691ae9a782c12260c94ed6bd1a63
Author: yosin <yosin@chromium.org>
Date:   Tue Feb 14 07:56:00 2017 -0800

Review-Url: https://codereview.chromium.org/2680943004

Hi yosin, could you please take a look and verify if the commit above could affect the speedometer's score. Thanks !

I found that the Chrome 58.0.3018.0 make the score decrease to original level.
This means it's fixed in some later commit in Chrome but ARC++ has not yet uprev to that version. I suggest we can leave this here until the ARC++ uprev to a new version of Chrome.

http://crrev.com/451270, landed on Feb 17, fixed speedometer score.

This appears to have been fixed back in Feb, but the bug wasn't closed.