I'm still getting the original sound on my Echoes.
I would assume that Amazon is changing something on their end. You can't affect it configuration-wise on Hubitat, and I don't believe it is something Hubitat can controll in the Hubitat skill.
I would guess this is possibly a test rollout of the new sound such that it only appears on some devices and not all. You might want to say "Alexa I have feedback" and report that you don't like the new sound. (or maybe you can do it in the Alexa app).
I'm noticing the same thing. It's happening at home and with the Alexa assistant in the car. It seems to have started yesterday. I think there's a team at Amazon titled "Customer Abrasion." They're good at what they do.