A bit of an odd one, but here's the steps to reproduce:
- Dock your Switch at the lockscreen
- Press and hold down the L or R button (maybe others work too, untested)
- Undock your Switch while you still hold the button
- When you see your lockscreen on the Switch, release the button
- Observe extremely slow UI navigation, making even unlocking impossible
I would say this reproduces every 2nd time. I checked Status Monitor and noticed core3 was stuck at 99.99% usage when this triggers, so I suspect it might be related. I've experienced this on FW 20.3.0/AMS 1.9.3 as well as FW 20.4.0/AMS 1.9.4.