I’ve just tested and IncrementInt doesn’t work if get the value from array int item (get function).
Could you provide a screenshot of the blueprint that you are using when you are seeing this issue occur?
Add 1 manually works
Using IncrementInt macro looks like buggy
I have been able to reproduce your issue, and have entered a bug report (UE-29529). I will provide updates on this issue as they become available. Thank you for your report.
The reason that this may not work is because you typically cannot pass the value of an array by reference, which is how that node works. So what it may be doing is not performing any of the functions of that node because it is unable to set the value of the element of that array.
In the meantime, I would recommend just using the +1 workaround that you have been using.
Have a great day