It could be missing IGMP Snooping Protocol support in a network with IPTV or custom VLAN setups. There are 3 versions (IGMP snooping (v1, v2, and v3)), managed

It could be missing IGMP Snooping Protocol support in a network with IPTV or custom VLAN setups. There are 3 versions (IGMP snooping (v1, v2, and v3)), managed switches have them all, unmanaged usually don't have them. To avoid problems, only pass a single VLAN to the unmanaged switch (it must be behind the managed switch for that), otherwise the unmanaged switch can and usually will bring a network down after some time. Or just use a switch with IGMP snooping support.