So I have the iptv network automatic setup and pointing at a URL of my m3u. I’ve selected it to not scan and set the service ID to 1. It imports everything under services and I’ve mapped with my EPG XML which is all working.
Does tvheadend redownload the m3u automatically to update channel changes, additions, or removals?
Yes. There is a setting in Network edit page called "Re-fetch period (mins)". It defaults to 60 but you can change it if you wish.