See https://git.tukui.org/elvui/elvui/issues/433#note_4934

this is not an issue with ElvUI. Greenwall just needs to get the update in place, and i've sent a fix to the author of Greenwall.

inside of Compat.lua of Greenwall (line 1: old, line 2: the "fix"):

-- gw.ChatFrame_MessageEventHandler = ElvUIChat.ChatFrame_OnEvent
gw.ChatFrame_MessageEventHandler = function(...) ElvUIChat:FloatingChatFrame_OnEvent(...) end
note: this will fix the compatibility issue in Greenwall and also fix it not having the ability to work in floating chats, which would have existed in previous versions.

note two: i don't personally use this a friend contacted me and asked if i knew it was an issue and told him i'd check it out. so, we just have to wait for the author of Greenwall now

Works here. Thanks!