i had the same problem. transfer the channels into another bouquets like the favourites bouquets or use a cron timer to run the script that populates your bouquets with the IPTV channels.
i think the reason it happens is that the IPTV providers script adds a script to run at boot up and the script doesnt get added for some reason. May not have permissions or something. i think this beacuse on a few of my recievers the IPTV channels get updated after reboot and i found a script that runs on boot up in /usr/sbin/<something>.sh