With the advancement of nanoindentation technology, more and more data are supporting that the pop-in event is not a homogeneous but a heterogeneous dislocation nucleation process mediated by vacancy-like defects. However, the conclusion is based on the two model-extracted parameters, activation energy and activation volume. There hasn’t been any experiment directly correlating the pop in event with vacancy activities. This work, following our previous nanoindentation study on a FCC high entropy alloy CoCrFeMnNi, aims to verify this correlation with specially-designed nanoindentation experiments. It was found that when the indenter was hold at a subcritical load (in reference to the critical load that triggers instantaneous pop-in) for a period of time, delayed pop-in was observed. Furthermore, the displacement bust size increased with the tip radius up to a few hundred nanometers. These two observations suggested the vacancy was at play because the vacancy can migrate under any applied stress and its number within the indented volume depends on the tip radius.