it's called shapping traffic, they apply it on big matches time, mean even if your client test his speed internet will find it fast (you will blame your server and show off about his internet speed), but when try to watch hd or full hd channels will get too much freeze, only can watch stable on low sd transcoded channel below 1 mbps. ( you need to transcode sport bundsliga channel below 1 mbps with 480p or 360p)
shapping traffic is smart filter to block iptv traffic on X time, clients on germany need time to understand the issue about shapping traffic, it's already happen on another country in europe, and now it's going to be bad, they (anti-privacy agencies operation black iptv) collect all dns hostnames iptv servers on big data base and they block it on match time. so your clients they can even ping to your main server.
Solution is VPN, client need to use VPN.