On rare occasions powerscheduler does not wake up the PC when recordings are due.
After having this problem three times in a week I decided to investigate it and I think I found the reason.

One of the last steps done before suspend is setting spawning a new thread. This thread aborts the old thread, sets the timer and then waits for the wakeup.

But the problem is that that the main thread does not wait for the timer being set, so it might be that the main thread ends, but the spawned thread has not executed.