in my case I think its a microwave / interference issue. I noticed that, when removing the front cover, the problems nearly disappeared. Maybe somebody can confirm this. The body moving parameter still shows strange signals but at least its a straight line, then after some hours it jumps to another value, remaining there for some time but the presence and movement signals look reasonable.
maybe modifying the front cover and / or adding microwave absorbing foam in the box. Absorption and reflexion are influenced by the material, the distance and the shape of this cover. Maybe fiddling around with these things could help. The influence can immediately be seen at the body movement parameter curve.
radom design (german)
unfortunately in german but google translate may help
they recommend a distance of lambda/2 between antenna and cover = 6.2 mm at this frequency. I measured around 11 mm in the kit. I will do some tests with this distance.