Win 10 Lags Resuming From Screen Saver Until Keyboard Used

This is really weird. I've never seen a computer do this before. It's a Dell E6540 laptop with the optional Radeon discrete graphics and Windows 10, fully updated. 8GB RAM and i7-4800MQ quad core. It's had this problem for months. I'm using a USB mouse and keyboard, but the whole system lags, not just the mouse.

When resuming from the screens being turned off from sitting, not asleep or hibernating, often it will be incredibly laggy, most obviously the mouse cursor giving about 1 fps until I use the keyboard. If I hit Ctrl-Shift-Esc to bring up the Task Manager, it stops lagging. I see 80% memory usage most of the time with several apps open, and below 10% cpu usage.

No antivirus aside from the Microsoft junk because I never download or visit websites that need it. I tried running Nod32 and MBAM which found nothing. I see no suspicious services or processes other than the AarSvc_3e7eb which seems to be legit from what I can find on Google.