I learned one morning that a cmos battery could become a resistor. It can fail in a way that it’s not working nor completely dead but passes just enough current to make a server motherboard that otherwise might A: Work, B: detect it’s dead/missing and boot anyway with defaults to instead C: just freeze and not do anything. That was a fun full day of time wasted.
Y’know the setting in the bios where you can choose boot on power restore, stay off or last state? This relies on a capacitor on the motherboard near the bios battery to store the last state. This 5 cent capacitor can die and sometimes behave like you are saying. I had a repair guy fix it cheap and that server worked normally after that.