[2020] Keyboard/mouse lock up when holding alt key down

I'm in discord and using the left alt key for push to talk. So I go into settings and unbind slow walk so that nothing is assigned to it.

I press the left alt key and hold it down. No response from any button on the keyboard or mouse. I can aim with the mouse, but with the left alt button held the keyboard and mouse buttons do nothing.

It's disappointing since that is only key I will use for my VOIP apps. It's even more disappointing since something like this should have turned up in rather basic QA.