Would 2 keyboards fail in the exact same way, with all caps and shift held down, but one is persistent after reboots and one isn’t? It doesn’t make sense.

Is this a typical pattern for keyboard controller failure that could be seen in this same way on two laptops at the same time?

I mean, I think it's much more likely that some hardware failed, than that someone executed a highly sophisticated attack that worked but ended up showing obvious signs of tampering.