@ian.heritage,
Take a look at the Power Meter view associated with the Freezer via the iOS/Android app. If you see it dropping to 0 on a fairly frequent basis (more than 1% of the time), then you are having communications issues between the Sense monitor and the smart plug. Could be a great many different reasons ranging from your WiFi network to the Sense monitor itself. FYI - the Sense monitor does NOT sync data with the Kasa, but instead the Sense monitor regularly (every 2 seconds) queries all the Kasa smart plugs on the same subnet for power information. They all report back in. If you see dropouts, in the Freezer Power Meter, you should contact Sense support - they have more diagnostics at their disposal.
The good news is that the Kasa protocol uses far less bandwidth than the Wemo flavor.