What are the output numbers that did not turn ON even though their online status shows as ON?
If they are output 5,6,7,8 then check if these are also double-defined as PWM or stepper motor output? A physical output that is defined as special function output will not work as regular output even if the corresponding "output" bit is ON.
If the output that are not behaving correctly are output 1 to 4 then these are linked to the expansion I/O signal as well as the 3 status LEDs. When you power cycle the PLC did any of the 3 status LED (one green, two red) turns on for half a second and then went off? If the status LED did not light up when you had the problem with the outputs then it is likely a hardware problem. You may like to replace it with a new unit and send the faulty unit in for an RMA inspection and repair.