Maybe the underlying alert for the build issue was going away, and that caused the problem?

From looking at the logs, it looks like you need to refresh your page. Your xrsf token expired, and so our server starts rejecting your requests.

We should surface this information better.

Perhaps we should add a full page autorefresh timed a bit before the XRSF token expire time? 

That totally fits what I saw.

The periodic updates to issues that you're currently doing is really nice, BTW.  It lets the sheriff just leave the page open at tab 1 and working off of it all day.

Asking the user to make a full page refresh is suboptimal.

Monorail has an ajax wrapper that attempts to auto-refresh the xsrf token under the hood when the server returns an unauthorized response code.  We should do something similar.  

 Issue 668210  has been merged into this issue.

I'll take a look at this.

Thanks Stephen! Here's the relevant code from Monorail you can use as an example. The js client has a function to silently refresh xsrf tokens so you can always just call CS_doPost() and be done with it:
https://cs.chromium.org/chromium/infra/appengine/monorail/static/js/framework/framework-ajax.js?l=44

And the server action it uses to do the refresh:
https://cs.chromium.org/chromium/infra/appengine/monorail/framework/tokenrefresh.py?l=24

Something similar in Go should be pretty straightforward. 

CL out: https://chromium-review.googlesource.com/c/414428/

The following revision refers to this bug:
  https://chromium.googlesource.com/infra/infra.git/+/1f968728d1e0de1acd5343fd37550d5ede5474ed

commit 1f968728d1e0de1acd5343fd37550d5ede5474ed
Author: Stephen Martinis <martiniss@chromium.org>
Date: Wed Nov 23 23:46:43 2016

SOM: Refresh xsrf token on post error

BUG= 665617 

Change-Id: If8f6c2d0b47359a97473252886f3ada8e1f72a3e
Reviewed-on: https://chromium-review.googlesource.com/414428
Reviewed-by: Sean McCullough <seanmccullough@chromium.org>
Commit-Queue: Stephen Martinis <martiniss@chromium.org>

[modify] https://crrev.com/1f968728d1e0de1acd5343fd37550d5ede5474ed/go/src/infra/appengine/sheriff-o-matic/elements/som-annotation-manager-behavior.html
[modify] https://crrev.com/1f968728d1e0de1acd5343fd37550d5ede5474ed/go/src/infra/appengine/sheriff-o-matic/elements/som-annotations.html
[modify] https://crrev.com/1f968728d1e0de1acd5343fd37550d5ede5474ed/go/src/infra/appengine/sheriff-o-matic/som/main.go
[modify] https://crrev.com/1f968728d1e0de1acd5343fd37550d5ede5474ed/go/src/infra/appengine/sheriff-o-matic/test/som-annotations-test.html

This will go out in tomorrow's weekly release.