I have the water pressure regulator set at 60psi. I sometimes see the pressure at 70psi or higher. I have a new regulator but don’t know why the pressure rises. I do have an expansion tank on the hot water heater that is less than a year old. Thought?
The regulator keeps the incoming pressure to 60. The issue you are seeing is probably caused after using hot water , the cold water in the hw tank is at 60 and now being heated so the pressure rises.
To prove this to yourself if the pressure is at 70 open a cold water tap for a few seconds, now the pressure is at 60, if the water in the hot water tank is heated there will be no change in pressure (not much anyway).
Next go run a hot bath or at least 5 gallons of hot water with the faucets off at first your pressure will be 60 but over the next 1/2 hour or so as the water reaches temp it will go up to 70 as you have observed.
This is normal and with that small swing I would say your system is working perfectly.