It’s not an issue with the Sense device. Read up on how Always On is computed - it uses data over the last 48 hours.
It will take something like 1/2 hour of zero usage in your house before Always On drops to zero (the lowest 1% of all the 1/2 second readings in the house have to go to zero, before Always On becomes zero).
Yes, the Always On calculation will also be “sticky” in the up direction. If you have had zero usage (or low usage) for along period, then start seeing a normal level of usage again, it will take time before Always On starts registering near your normal level. How long will depend on the “population” of the 4836002 = 345.6k Total Usage samples from the last 48 hours.