I bet the ones that stopped working were models where the manufacturers didn't really do their job correctly when reverse engineering how the original dock works.
the official Dock was not updated, meaning any Dock that processes the signals the same as the official one, will automatically also still work.
I wouldn't be surprised if the ones that stopped working were never tailored specifically for the Switch 2, and were just recycled USB-C docks that the manufacturers happened to notice already worked with the Switch 2... so they just stuck the already finished hardware into a different housing that fits the Switch 2 and called it a day.