QueryAuctionItems not working

[S4m]

Hello, I'm new to addon development and can't get QueryAuctionItems to work. (it's for WoW Classic).

AUCTION_ITEM_LIST_UPDATE fires when searching manually, but not when programmatically queried. However, "AH is queryable" is printed. On a super rare occasion it has worked, and I have no idea why. The code is below, surely I'm doing something wrong.

Sandbox = { }

-- Code ...
local frame = CreateFrame("FRAME");
frame:RegisterEvent("ADDON_LOADED");
frame:RegisterEvent("PLAYER_LOGOUT");
frame:RegisterEvent("AUCTION_ITEM_LIST_UPDATE");
frame:RegisterEvent("AUCTION_HOUSE_SHOW");

-- Slash Commands ...
SlashCmdList["SANDBOX"] = function()
    print("Slash Sandbox");
    frame:QueryAH();      
end
SLASH_SANDBOX1 = "/sandbox";
SLASH_SANDBOX2 = "/sb";

function frame:OnEvent(event, arg1)
    if event == "ADDON_LOADED" and arg1 == "Sandbox" then
        print("Sandbox");
    end

    if event == "AUCTION_ITEM_LIST_UPDATE" then
        print("AH update");
        batch,count = GetNumAuctionItems("list");
    end

    if event == "AUCTION_HOUSE_SHOW" then
        print("AH show");
        frame:QueryAH();
    end
end

frame:SetScript("OnEvent", frame.OnEvent);

function frame:QueryAH()
    if CanSendAuctionQuery() then
        print("AH is queryable");
        QueryAuctionItems("", nil, nil, 0, 0, 0, 0, 0, 0, 0);        
    else
        print("AH is not queryable");
    end
end

Much appreciated.