I’ve been struggling with this issue for months now and had resorted to unplugging the laptop before putting it to sleep. By sheer coincidence, I noticed that Windows used 20% of one core when I didn’t move my mouse for a few minutes, and stopped as soon as the mouse moved. Turns out Windows runs its own version of memtest when idle! This is started by 2 scheduled tasks under Microsoft → Windows → MemoryDiagnostic.
Lo and behold, it’s this same task that gets triggered by putting the laptop to sleep. “Modern” standby indeed. Of course it’s a great idea to peg a cpu checking memory when the computer is sleeping, of all things /s. So, try disabling the memtest scheduled tasks.