Most likely just try again after a while.
Or comment out line 4 in /etc/pacman.d/chaotic-mirrorlist, try again, uncomment.
Did it happen to me once too many? Handy scripts you'd like to share - #91 by meanruse
Oh wait, I see there’s an update for chaotic-mirrorlist.
Maybe try pacman -S chaotic-mirrorlist first.
It’s working here, likely some of the regional mirrors was just caught while updating itself.