This is something I ran into because of recursion issues. I attempted a fake, but succeed at a very hacky while loop that is like an IEnumerator yield return. It's a bad hack though. As I have to embed each graph to make it an instance, while constantly checking a variable is true with Update, to allow it to enter a conditional loop.
I'd assume all updates must constantly be running in each one, while the game object is enabled. That's a lot of individual Update checks constantly happening everywhere just to see if it can loop.
I'd either suggest more Control units for conditions and time based loops, or my other suggestion is Graph level event calls. Call the event inside the while loop graph I make, when you get to it, and call another event to call the original to re-enter every frame. Eventually the condition becomes, not true, and the event is no longer called and it passes. To an exit node. Nothing being called every frame other than when the loop happens.
I'm sure there is more you could do, but that's my first major run in with this limitation. Does this make sense? Not at my computer, but I can provide photos of it if necessary.
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