So, I connect DC generator to the input (Vin) and oscilloscope to the output (Fout) of this circuit.
If I set Vin to 1V - I get nothing on output (Fout).
If I set Vin to 2V - I need to wait few minutes until input voltages will be at the same level and then I can see output signal (Fout).
If I set Vin to 3V - I get output signal (Fout) instantly at the start of simulation.
If I set Vin to 4V - I need to wait minute/two until input voltages will be at the same level and then I can see output signal (Fout).
If I set Vin to 5V - I get output signal (Fout) instantly at the start of simulation.
If I set Vin to 6V - I get output signal (Fout) instantly at the start of simulation.
If I set Vin to 7V - I need to wait 5-6 seconds until input voltages (on the right op-amp IC) will be at the same level and then I can see output signal (Fout).
If I set Vin to 8V, 9V and 10V - I get nothing on output (Fout).
Any ideas?