Rugosa Map Boss Stuck After Song Phase

Song phase finished. Boss map icon still hanging out below the arena, nothing else happening. No Abyss in boss room, just decided not to work anymore.

I had something similar happen with the crow bell map boss. First phase of the boss brought it down to half and then instead of walking to the next area where the bell is, it became invulnerable and kept trying to fight me and never finished phasing.