It depends on who your ISP is and who you get your IPTV from.
Virgin, BT, Sky etc. are actively trying to block the ip addresses of the IPTV servers, the larger ones are more likely to be targeted. It's then a case of the IPTV folk looking for a work-around, usually, they move to a new server or IP address.
Sometimes they'll hit the servers that provide the steams for the feeds, you'll know this when you can stream box sets and movies but can't watch any channel.