I regularly use a key chord which uses “shift” + “alt” keys on right side of my Model 01. I am experiencing regular “missing” key up events from the keyboard for the alt key. If I press another key it will register the alt key up after the first button press.
I believe this may be a key scanning glitch with the particular combination of shift+alt+ which is picked up on the next scan triggered by a keypress (but this is an uninformed conjecture). Possibly triggered by a chattering key? I have not explicitly cleaned the key contacts yet.
Here is an event log from karabiner-elements eventviewer tool. This occurs even with karabiner-elements not running. Keyboard is connected via hub to a USBC docking station to Apple Macbook Pro M1.