Joycon (left) indicator lights flashing an unknown error code

I just replaced the joystick on my left joy con, Using the joystick from a broken (in non-joystick related ways) left joycon. The joystick part of the equation works perfectly.

However the SR, SL, and sync buttons seem to have stopped functioning. And even more worrying, when not connected pressing a button does not cause the indicator lights to race up and down as one would expect. Instead there is a repeated flashing pattern of the first, third, third lights from the top.

This is frustrating as I need the sync button to be able to pair the joy con to a computer. I don't know if the sync/sr/sl buttons failing and the flashing are related. The joy con works fine when I connect it to my switch, and works fine wirelessly after I've connected and paired it. But the physical connection isn't an option for pairing with a laptop.

Here is what I'm observing, to be clear:

And for reference, this is what I would expect (video is of my right joy con):