Chat Lag affects all Group Chat, including Conference Chat, seemingly with no rhyme or reason.
There are times that Group or Conference Chat can fail entirely, and in some cases there is an explanation: each Group UUID determines which of the 16 chat servers will be used to handle delivery of text. A Conference Chat is also assigned a Temporary UUID for this purpose. The first character of the UUID (0-9, a-f) directs the chat to the tasked server.
If a particular server is offline, all Group and Conference Chat tasked to that server will fail. A ticket submitted to LL is the only way to remedy this situation.