I got this reply from someone outside of Stack exchange, so I'll post it here to help others
Searched the code for bAlwaysResetOnEntry, looks like its used for animation state machines.
Implies its possible to re-enter a state while it is still the active state, and the reset flag would cause the state to re-trigger, possibly re-calling the OnStateEntered events.
if ((!bAlreadyActive || bForceReset) && !IsAConduitState(NewStateIndex))
// Initialize the new state since it's not part of an active transition (and thus not still initialized)
// Also call cache bones if needed
// Note dont call CacheBones here if we are in the process of whole-graph initialization as a 'never updated' counter
// will not perform its 'minimal update guard' duty and every call will end up getting though, performing duplicate work
// over Save/UseCachedPose boundaries etc.
// This is OK because CacheBones is actually called before updating the graph anyway after whole-graph initialization
bForceReset is assigned bAlwaysResetOnEntry earlier.