[xubo]

1. I already had bugcatcher/bugsack installed and been using it a lot. No errors pop up when it misses data.
2. I've added the code below (has no effect on the outcome).

local EventFrame = CreateFrame('Frame')
EventFrame:RegisterEvent('ADDON_LOADED')
EventFrame:SetScript('OnEvent', function(self, event, ...)
    if self[event] then
        self[event](self, ...)
    end
end)
 
function EventFrame:ADDON_LOADED(name)
    if name == "MCL" then
        if not IsAddOnLoaded("Blizzard_Collections") then
            UIParentLoadAddOn("Blizzard_Collections")
            print("LOADING COLLECTIONS")
        else
            print("Already Loaded")
        end
        SLASH_MCL1 = "/mcl";
        SlashCmdList.MCL = core.Config.Toggle;
        core:Print("Welcome back", UnitName("player").."!"); 
        -- remove event
        self:UnregisterEvent('ADDON_LOADED')
        self.ADDON_LOADED = nil
    end
end

Have I done that correctly? This has had no effect on the original issue.