Adding a dialog box in a cusomization disables javascript from another dialog box.

This should solve your problem:

public OpportunityMaint_Extension : PXGraphExtension<OpportunityMaint>
{
    public override void Initialize()
    {
        base.Initialize();

        // Add the Page_Load event handler
        var page = System.Web.HttpContext.Current?.Handler as PX.Web.UI.PXPage;
        if (page is object)
            page.Load += Page_Load;
    }

    // Executes the PXAddressLookup script which is broken by the page customization
    private void Page_Load(object sender, EventArgs e)
    {
        var page = (PX.Web.UI.PXPage)sender;
        PX.Objects.CS.PXAddressLookup.RegisterClientScript(page, Base);
    }
}