There is a limit to resources in the ESP8266. How it handles each unique situation is a function of the demand placed on other resources. The goal is to have it handle a reasonable load and fail without crashing.
I wouldn’t classify 60 measurements as a reasonable load. There is no practical difference between Wh and KWh. They are the same measurement. While VAR and VARh are useful as parameters to billing on the mains measurement, I don’t see any value in that data for branch circuits. PF will give an indication of loads with high VAR.
As a practical matter, one frame of 60 measurements could be 4-6K of data, which pushes other limits.
I’d recommend you scale back your schema, and if you are going to have a lot of measurements, limit the length of any names used and the number of keys associated with each measurement.
If you really need all that data, an alternative is to use a second IoTaWatt and divide the load between them.