Booting self-built ReactOS x64 Live CD version 0.4.15-dev-2882-g76ce08dcec in VirtualBox (see environment for details).
The problem is fully reproducible for me and it's not possible to skip it.
Debug log attached: windbg.log
You want to look at the event pointer, establish whether it's on the stack, and if so, which thread's stack.
The easiest way to cause this is that a function that was supposed to wait on the IRP to complete returned early. So the event on the stack is no longer valid.
(this assert is absolutely fatal and if you ignore it, anything you do beyond that point is useless in terms of debugging)