This happened while sheriffing yesterday, on Tue 6/5 11:33am PDT.

I saw many alerts under "Consistent Failures", and some others as well (and I was in the process of filing a bug on one of them).
A few minutes later, it seems that SoM had auto-refreshed, and most of the alerts had gone! The whole "Consistent Failures" section had disappeared, and the main alerts went down to just 2 Pri-1 and 1 Pri-2.

I kept hitting the browser Refresh button (and opening SoM in new tabs), to try to get all these alerts back again, but it didn't work. I even remarked to my co-sheriffs about how almost all of the SoM issues had gone, and that perhaps we didn't have to worry about them any more :)

About 5 minutes later, SoM updated again, and all those alerts re-appeared.

As an example,  bug 849388  was attached to an alert that was affected. It linked to this builder:
https://ci.chromium.org/buildbot/chromium.memory/Linux%20ChromiumOS%20MSan%20Tests