this is usually an outcome of your internet and networking.
As mentioned, someone using same interenet to use netflix or other similar like XBox would cause that.
Downloading torrents would cause that.
Bad or insufficient quality connections would cause that.
Networking priority or interuptions from ongoing PC/internet tasks can be a cause.
There are many reasons why you'd get freezing using iptv , most are not iptv server related (some are thou, for sure)
Could it be a MAG receiver issue ?
I doubt it but maybe, if box is running software known to be an issue.