[Fizzlemizz]

Try moving OnReady from ADDON_LOADED to PLAYER_LOGIN. Your SavedVariables will have been loaded by the game when this event fires and it only fires once.

Don't forget to remove your old SV .lua file(s) before trying.

function BattleDex.OnReady()
    -- init database
    if not BattleDexDB then
        BattleDexDB = {
            pets = {},
        }
    end
    if not BattleDexPrefs then
        BattleDexPrefs = {}
        for k,v in pairs(BattleDex.default_options) do
            if not BattleDexPrefs[k] then
                BattleDexPrefs[k] = v
            end
        end
    end
    GameTooltip:HookScript("OnTooltipSetUnit", BattleDex.AlterTooltip);
end
 
function BattleDex.OnEvent(frame, event, ...)
    if (event == 'PLAYER_LOGIN') then
        BattleDex.OnReady();
    end
 
    if (event == 'PET_BATTLE_OPENING_DONE') then
        BattleDex.RecordBattle();
    end
end
 
-- ...
 
BattleDex.EventFrame:RegisterEvent("PLAYER_LOGIN");
BattleDex.EventFrame:RegisterEvent("PET_BATTLE_OPENING_DONE");