I’ve not used this specifically, but I suspect what’s going on is you’re calling something that’s changing the array out from underneath the “ForEachInstance” function. I’m willing to bet it was not written/intended to be used in this manner. Think of just a normal for loop through an array. You wouldn’t want to change the size of the array inside the loop itself. Make sense?
Looking at the API I don’t see a nice way to do what you want, however, maybe you could add the handle to a local array and then iterate over your local array calling RemoveActorInstance? As a side note, your lambda is not returning anything when the handle is valid.