Hello, I had a similar problem with the sum sensor. I am attempting to track my PC energy use (which isn’t switched on all the time) using openhardware monitor but I found the values would jump unexpectedly when I turned my PC on.
After reading this thread I added a trigger to my template sensor so it updates every second (even if the value is 0) and it seems to have solved my problem with the riemann sum sensor.
Hopefully this helps you with your problem.