Last one for today. Somewhere after updating to 2.4 and/or disabling the cron stuff (removepackage-cron) my sync_folder is now owned by my main user, not btsync as it was previously.
I noticed this when I looked at btsync and saw it could not write to any folders. I found some help online, by doing this:
sudo setfacl -R -m "u:btsync:rwx" /home/your_username/btsync_share
This resolved it for me (though did not change the way its listed via ls -l).
Add this into your list, but it might be me, etc. I did do a handful of reboots of the server today for other things, but nothing involving permissions/etc (though I think the updater does?)