Why does rsync sometimes fail to overwrite the local files

I have a script called copy-site which I use to copy a site from the production server to my local machine. copy-site example.net/httpdocs/ example.local/httpdocs/ will do a dry run rsync; adding a third parameter of true does the copy for real.

Sometimes, the local files have been edited. In this case, I want rsync to throw away my local edits, overwriting them with what's on the server. However, often it does not do this. Nor does it show anything relevant in an error log. I tried redirecting stderr to a log file, but it's usually empty or contains warnings about directories it cannot access on the remote server; it says nothing about not overwriting certain files. And certainly it can access those files: if I delete the local copies, and then run it again, it creates them fine, as a perfect copy of what they are on the server.

I added the -I flag today, but it made no discernible difference.

#!/bin/bash

if [ "$3" = true ]
then
    echo "real rsync";
    echo "deleting files";
    find $2 -type f -name ".*" -delete;
    echo "rsync running now";
    rsync -avziI --verbose --exclude-from /home/trig/copy-site-exclude -e 'ssh -p 2201' trig@server.example.net:/var/www/vhosts/$1 $2 --append-verify --delete;
    notify-send -i "$([ $? = 0 ] && echo terminal || echo error)" "copy site" "rsync complete";
    echo "setting permissions";
    chmod -R 0777 $2;
    notify-send -i terminal "copy site" "full permissions granted";
else
    echo "dry run rsync";
    rsync -avziI --verbose --exclude-from /home/trig/copy-site-exclude -e 'ssh -p 2201' trig@server.example.net:/var/www/vhosts/$1 $2 --append-verify --delete --dry-run;
    notify-send -i terminal "copy site" "dry run complete";
fi

copy-site-exclude is merely a list of image thumbnails (identified as beginning with dots), which I don't care to transfer as they can be regenerated locally.

custom/public/images/.*.jpg
custom/public/images/.*.png
custom/public/images/.*.gif
custom/public/images/.*.jpeg

What flags do I need to pass to rsync to make it discard all local changes, so that my local folder is a perfect reflection of the source folder on the server?

Local OS: Ubuntu.
Server OS: CentOS.