Curtaros normally stops singing his song to the group once you talk with each of them to completion.
He does the whole sequence with the group repeatedly even when it has been finished if you come into the game in the crafting area in Alinor however. That should only happen if you have not already talked to everyone. He won't normally do that if you have talked to everyone, no matter how many times you run in and out of the crafting area, but always does when you start there. PS4 if it matters.
I do get the rare time he sings when not present, but that may be tied to not having talked to everyone in the group. None of the group nor Curtaros is present when he sings this way however. This is a second bug and not the more annoying repeated sequence.
PC
PS4/PS5