[Garkin]

I have just a quick look to the addon code and there is virtually nothing to fix, it should be working just fine. I will check it in game.

Only thing I do not like is replacing of the original function of CHAT_SYSTEM instead of hooking it.
Instead of the last function in the code. I'd rather use this hook (but it is matter of personal preference):

-- Hook the original function so we can fix the anchors
local TransferWindow = CHAT_SYSTEM.TransferWindow
function CHAT_SYSTEM.TransferWindow(...)
    -- First, do what the original function did...
    TransferWindow(...)
 
    -- Second, fix the anchors so the text is visible
    if container ~= CHAT_SYSTEM.containers[1] then
        ChatMultiWindow.FixContainerAnchor(container)
    end
end