From time to time my emonpi device dashboards fail to correctly show the total khwd used for the odd day or two in any 30 day period, yet if I look in the graph data view it clearly shows that it got measurements through-out the day in question.
It happens on all 3 of my installed devices on random days - each of them located at different sites and it does not appear to be caused by any power failure or similar event.
That seems fine, is there any difference between using the cumulative kwh: use_kwh feed and the emonpi:kwhd feed? you can use the first using delta mode and it may give better results… my other thought is perhaps a timezone related issue, are you using emoncms.org or a local instance?