[circonian]

As merlight said ZO_DeeptableCopy doen't copy metatables. Just copy from/to _G instead of trying to copy SimpleXPBar.AWSV or SimpleXPBar.CharSV
and you don't need SimpleXPBar.accountwide_settings, you can use SimpleXPBar.AWSV

Warning: Spoiler

local function OnAddOnLoaded(event, addonName)
    if addonName ~= ADDON_NAME then return end
    
    local defaultsA = { }
    local defaults = { }
 
    TestAddon.svt = {}
 
    TestAddon.sva = ZO_SavedVars:NewAccountWide("TestAddonSavedVars", 2, nil, defaultsA)
    TestAddon.svc = ZO_SavedVars:New("TestAddonSavedVars", 2, nil, defaults)
        
    TestAddon:LoadSavedVars(TestAddon.sva.accountWide)
        
    TestAddon.CreateSettingsMenu(TestAddon)
    
    EVENT_MANAGER:UnregisterForEvent(ADDON_NAME, EVENT_ADD_ON_LOADED)
end
 
 
--[[
You don't need to do a copy here, only copy in the settins menu
when the user toggles from accountWide to Char, that way 
they get the most up-to-date version of the accountWide
saved vars and it doesn't run copies anymore than necessary
--]]
function TestAddon:LoadSavedVars(useAccountWide)
    if useAccountWide then
        TestAddon.svt = TestAddon.sva
    else
        TestAddon.svt = TestAddon.svc
    end
end
 
 
[1] = {
    type = "checkbox",
    name = "Use Account Wide Settings",
    default = true,
    getFunc = function() return TestAddon.svt.accountWide end,
    setFunc = function(bValue) 
        TestAddon.sva.accountWide = bValue 
        if not bValue then
            local sDisplayName = GetDisplayName()
            local sUnitName = GetUnitName("player") 
            -- TestAddonSavedVars = your addons saved var table name
            -- from your manifest
             ZO_DeepTableCopy(_G["TestAddonSavedVars"]["Default"][sDisplayName]["$AccountWide"], _G["TestAddonSavedVars"]["Default"][sDisplayName][sUnitName])
        end
        self:LoadSavedVars(bValue)
    end,
},