Hi, as far as I know the sight sense will give you an update when an actor is no longer in sight (WasSuccessfullySensed() being false then), but will expire after the max age (or never if the max age is set to zero).
What is the max age you have for the sight sense?
As you can see, IsExpired does not output 1 when the character goes out of the field of Sight (green area).
It should become expired after max age time has passed since the character went out of the field of sight (for max age being not zero). If you want to know when the character goes out of the field of sight, you can check WasSuccessfullySensed() in the Stimulus, in your OnDetected function (in your function there, replace Stimulus.IsExpired(), by Stimulus.WasSuccessfullySensed()).