The problem is not related to drip feeding or the 021 error.
This is speculation on my part, but it sounds like pressing the Control Reset button caused a DC output to turn on (or off), which then caused a relay coil to turn on (or off). This action caused a short in the +24VDC and the entire power supply "crowbarred" or shut down. This is why the screen went blank.
The power supply would have reset when you cycled power on the machine, but one of the side effects of the sudden shutdown was apparently to lose part program memory and tool offsets. This may indicate a bad backup battery.
I think you need to find what is shorting out when you press the Control Reset button. You could start by connecting a meter to the +24VDC and recreating the problem to verify that the +24VDC is indeed going to 0VDC.