Mortal Coil: Adrenalin Intelligence (1995). "Normal" difficulty. Part 4.2.

Started mission four from scratch and this time managed to complete it - previously mentioned door was open and card "C" was behind it. This time I've pressed only one switch that required to proceed further and get card "B", while also made direct cuts to the keys, no exploring. Not sure what specifically matter here or it was just an another weird bug of this old title, but now can deal with the next mission.