Umb 7.13.1 upgraded from 7.5.4

Could someone please tell me what has changed between 7.5.4 and 7.13.1 to prevent the following macro from displaying in an RTE? Error is indicated in the code:-

@inherits Umbraco.Web.Macros.PartialViewMacroPage
@using ContentModels = Umbraco.Web.PublishedContentModels;
@{ 
    var assetId = Model.MacroParameters["asset"];

    dynamic asset = Umbraco.TypedContent(assetId);
}
@(RenderAsset(asset))

@helper RenderAsset(ContentModels.MacroAccordion macroAccordion)
{
    var accordions = macroAccordion.Accordion.Select(x => new ContentModels.Accordion(x));
    foreach (var accordion in accordions)
    {
        <div class="accordion">
            <header><h3>@(accordion.Title)</h3><span class="icon-icon-small-arrow-up"></span></header>
            <div class="accordion-content">
                @(accordion.Content) <<<< Error : 'Cannot render a macro when there is no current PublishedContentRequest.'
            </div>
        </div>
    }
}

accordion.Content "can" contain another macro (not the same macro) and displays perfectly on the original site when it does.

Any clues how to make this work again would be appreciated.

Many thanks.

Craig