I was trying to install python2 and rsync. Running apk add python2 created a symlink named python2 to an empty file it created named python2.7. Running apk add rsync created a file named rsync that had the same size as the rsync binary, but running hexdump on it revealed it to be full of zeros.

The workaround for now was to uninstall those packages with apk del and reinstall.