DSO Quad suggestion and bugs.

Hi! I need help.
My device gives out the wrong form of a signal on the channel “A”. I repeatedly changed an firmware, the result on all is identical. I understand that malfunction is not in the program, and in the hardware. I ask to prompt to me, what details on a payment can be faulty?
I changed the probes, it didn’t solve a problem.
On a screenshot both channels (A and B) are connected to the same signal, only shifted for the period