I just converted my devices to V2 devices and found that key items required are either accurate/working or the value is wrong and -1.
I found the issue: USE STACK SIZE doesn’t convert its value to it’s V2 device. USE STACK SIZE ends up being -1 in a conditional button when converting devices to V2.
Thank you for your report! We would like to look into this further, would you be able to submit a bug report using the form available here: Fortnite Creative