Sorry, not meaning to appear difficult to please. I'm very pleased with my LR!
Anyhow, from looking at the pressure readings in the app I figured out what is going on. The pump is just doing its job and kicking in when the pressure drops below the set point. With my usual PI range of 2-3.5 bar it doesn't happen that often, but the pressure does fall that low from time to time. Moving the PI pressure to 6 bar causes the behaviour more frequently. Normally the pressure is around 8-12 bar.
The original question from me was whether the low pressure in the system might mean I have a piston seal leaking slightly. Is that possible, or is the occasional drop to below 3 bar normal? In my case with the expansion valve isn't an issue as I am getting the occasional check valve warning.