Here’s something funny i found in UE.
So maybe you have heard about observer effect, if not here’s wikipedia segment:
“Observer effect (physics) In physics, the observer effect is the theory that simply observing a situation or phenomenon necessarily changes that phenomenon. … An especially unusual version of the observer effect occurs in quantum mechanics, as best demonstrated by the double-slit experiment.”
So i found that something similar is going on in UE4. I was checking something in my BP and i created this:
https://forums.unrealengine.com/core/image/gif;base64
Whenever i hit H on my keyboard it prints timestamp + true or false.
And here is the funny part.
When i repeatedly hit H the output looks like this:
https://forums.unrealengine.com/core/image/gif;base64
So it changes from true to false after ~1,9s.
BUT!
When i plug the print node to Event tick so i can see it bettter…
https://forums.unrealengine.com/core/image/gif;base64
The value stays true forever!
What is goint on?
I noticed something similar earlier in other project. I was doing some bug hunt, my character was not moving after a while. When i was playing in main window the bug was there everytime. So i switched on my second monitor, i put my BP there so i can watch what is going on in real time. BAM! Everything was working great, no bugs at all.
Switched off second monitor and returned to watching game playing in main window…character stops moving, the bug is there once again. And it was working like this everytime.
Funny isn’t it? 
Does anyone have some explanation on this?
Kavaar