As a follow up to my question (see circuit diagram there), I am thinking further if I may be a cause of the problem. My idea that the second part of op-amp and another op-amp chip may have been damaged because, at some point in time, I did not connect their positive inputs, and was "hot-" connecting these inputs to the signal source on the same board.
I think it is very low probability, as initially, when things did not move properly, everything was connected, but anyway worth checking.
I saw this and this. My chips did not heat (I was checking it almost every time when operating them), no smoke and no craters up to physical damage. All op-amps were configured as voltage followers all the time, thus, as I understood, must drive output to some specific level, not saturate or get to "latch-up" situation.
Am I correct?
Update: op-amp is AD8512A (this info is available in my original question).
@PlasmaHH: looking to datasheet I see
The AD8510/AD8512/AD8513 have internal protective circuitry that allows voltages as high as 0.7 V beyond the supplies to be applied at the input of either terminal without causing damage
No word about unconnected input pins, or floating input pins.