Motor connected to M2 pin does not react to forward command but react to backward command correctly. There is no problem with the motor connected to M1 pin. M1 moves forward and backward properly.
I switched to motors (by plugging motor#1 into M2, motor#2 into M1). motor#1 connected to M2 pin did not move forward,but move backward.
I created a project in mBlock to see behavior of the motor connected to M2. When forward commanded, motor did not move, just stopped. When it is being backward commanded, motor moved backward as expected. I replaced batteries, it did not help.