I have no idea, what you mean by AV sandbox mode, I opened the game normally through executable file, and I don't think I was having any issues with FPS.
Some Anti-Virus Softwares have a sandbox mode for non-trusted programs.
I've located the only place where this could've happened, its in the spawn soldiers loop event, where a race condition can happen if the Game don't have enough resources and it skips the event that stops the spawn loop.
