To me it looks like ES returns only part of the search results. I have had the same. You can try relaxing ES search timeouts, and look if it helps. Anyway; when the dashboard widget refreshes automatically, these missing values might jump in and make the graph smooth (if this is the problem in your case).
Sadly that’s not the issue. The dips-to-zero in the graph are unwanted, but expected as the Heroku log drain provides data minute by minute, but not necessarily ON every minute. You’ll notice in the histogram that there’s a good block of one message per minute, and around the gaps, the following or interim minutes have two messages.
The issue the topic is about relates to the differences between the blue line, whose data is being rounded to the nearest 0.5 and the red and green lines whose data is being displayed as it is stored.
Probably a bug, but a transient one and most likely elastic search related. Once the index rolled over last night at 00:00 UTC the values started displaying correctly in the graphs & quick values as well as in the field text.
Possibly related to receiving some aberrant value at some point in that index, but all the values that display show up as the expected numeric value. Marking this solved and chalking it up to code ghosts.