Brightness randomly changes

Since a few weeks I am experiencing strange behaviour of my led lights. I have 2 sets of 4 led lights in my livingroom, both driven by Fibaro Dimmer 2 modules. The brightness randomly changes as you can see in the attached graph. As for as I can see there is no flow that could be responsible for this. I have 1 flow to enable the lights at sunset and 1 flow to disable the lights at 23:30h.

Is there someway to inspect or monitor what causes the brightness change?