Before launching the game, you first need to enable the console or you won't be able to input the fix command. Right-click Alyx in your Steam Library, go to Properties, and type the following in "Launch Options:" -console -vconsole



Now simply close that window and launch the game.

The bug typically occurs when loading a save game but could also happen during a map cycle. Once you get the hang of fixing it, you can do it quickly and easily.

As soon as you notice the AI is disabled, pause the game, take off your headset, press ~ on your keyboard (or whatever you have bound to open the console), type in "ai_setenabled 1" without the quotes, hit enter, put your headset back on, unpause, and you should be good to go. You can choose to exit out of the console if you like. If it happens again, just open the console and press the up key to display the last command. It will remain there in the history between playthrus so you'll likely never have to remember it again. Pressing up and down multiple times in the Command field cycles thru the history.