Looks like all bug filing from Sheriff-o-Matic is broken. I believe this is related to a general issue with Monorail that happened earlier this week as the result of an endpoints API upgrade. 

That makes sense. I was pretty sure I had been able to file one on Tuesday, so when the first one I tried today failed, I presumed that it was because I was trying to file an infra bug.

 Issue 866207  has been merged into this issue.

I'll try to fix this issue either today or tomorrow. At the very least, since it seems like inline bug filing often ends up being buggy, I think we should add a fallback to file a bug directly through Monorail with autopopulated data. 

 Issue 867064  has been merged into this issue.

The following revision refers to this bug:
  https://chromium.googlesource.com/infra/infra/+/3ffebc1877187468c343d493f088a22816cce560

commit 3ffebc1877187468c343d493f088a22816cce560
Author: Tiff Zhang <zhangtiff@google.com>
Date: Wed Jul 25 17:17:14 2018

SoM: Fix inline bug filing.

Demo: https://16663-3917a8b-tainted-zhangtiff-dot-sheriff-o-matic-staging.appspot.com/
Example of bug filed: https://monorail-staging.appspot.com/p/chromium/issues/detail?id=621171

Bug:865456
Change-Id: I51fcb0125bc0977b1d5ae0804d926bd0fe1c8d5f
Reviewed-on: https://chromium-review.googlesource.com/1147755
Commit-Queue: Tiffany Zhang <zhangtiff@chromium.org>
Reviewed-by: Sean McCullough <seanmccullough@chromium.org>

[modify] https://crrev.com/3ffebc1877187468c343d493f088a22816cce560/go/src/infra/appengine/sheriff-o-matic/som/handler/annotations.go

A fix for this should have landed last week.