Sending data to streaming dataset not always successful

Hi,

I'm trying to recreate what Charles Sterling describes in his blog post here:

https://blogs.msdn.microsoft.com/charles_sterling/2016/10/17/how-to-create-and-customize-applications-with-powerapps-with-laura-onu-webinar-1020-10am-pst/

...but instead of using Flow, I'm calling the web service from Excel using Power Query. I have the Historic Data Analysis option turned off. The strange thing is that the data in the dataset only seems to be updated about 50% of the time. On my side everything seems to be working ok: the calls to the web service always succeed, and I can see them sending what I expect using Fiddler. I'm also nowhere near the published limits for the API (https://msdn.microsoft.com/en-us/library/dn950053.aspx). It's just that my dashboard tiles don't always change with the new numbers. I can't see a pattern either: sometimes it works, sometimes it doesn't, although it does seem more likely to work after I have not made any other requests for a few minutes. Is there some unpublished limit that I'm running into?

Chris