Re-sort your Arch mirrors using the welcome application.
Find better mirrors (which is what the ranking should do) or improve your connectivity if basically everything is failing. I realize that may or may not be possible.
It’s also true that mirrors are used as a distributed system and as long as at least one responds, you’re fine.
Ah, about that, I deleted that app 
What other method can I use?
Install rate-mirrors if it isn’t already installed and then run:
rate-mirrors arch --max-delay 7200 | sudo tee /etc/pacman.d/mirrorlist
Well, if you KNOW (sight unseen), then you can manually edit your mirrrors. Of course if you know that, you probably can just write the binary updates yourself.
Otherwise, reinstall it.
I get issues like this a lot due to how I can connect to the net, I just restart the processs tbh (I know what is causing it, I cant fix it so I just keep trtying lol)
Also keep in mind pacman will try other mirrors when it can’t retrieve a file from a mirror. While I’ve had the occasional mirror failure, I’ve never been left in a partial-upgrade situation since it rolls to the next mirror on the list. Which explains why it’s a list, not a single entry.
Check your pacman log and you’ll see the failed file was actually installed because it was subsequently retrieved from another mirror.