Did you purchase the Sub (Gen 3) new or used? Were you able to successfully move the other Sonos speakers to S2?
Sometimes things get odd and a power-cycle of all Sonos (together) and a router reboot will get you back to more normal operation.
I’d verify the S2 update worked properly and then try adding the new Sub again.
Maybe move the old Sub to a different room to get it out of your way?
What are you trying to connect the Gen 3 Sub to?
I have an older Sonos system and just bought one more sub (gen3)
I tried to update to S2 and at the same time i updated the speakers to fit this while trying to add the 2nd sub. I am not able to install the 2nd sub. I dont even see it when trying. (Frustrated)
Has anybody tried this with success? I disconnected the 1st sub and tried to install the 3gen sub. Still didnt see it.
@Tvtitteren , if you bought the sign used chance are the seller didn’t reset it before selling it so try doing a factory reset on the sub, that was the fix on a open box Beam I just bought.