Cannot change trigger level?

I have a very strange problem: I cannot seem to change the trigger level anymore. If I set the oscilloscope to one shot I see the trigger indicator with value 0.00 rising. I can move it up by dragging the header with my finger, but that just seems to move the Y axis: the value stays at 0.00...

This is on an iPhone. Also tried on an iPad: same. Pokit pro, Hardware V1.0, Firmware V2.0.2.