refresh() does not add CSS classes

[sqwk]

I am checking if new elements have been been added to the DOM to call refresh():

    const solutionList = document.getElementById('solution-list');
    if (solutionList != null) {
        const observer = new MutationObserver((mutations) => {
            mutations.forEach((mutation) => {
                mutation.addedNodes.forEach((addedNode) => {
                    if (addedNode.nodeName != "#text") {
                        BackgroundCheck.refresh((addedNode as HTMLElement).querySelector('.solution-title'));
                    }
                });
            });
        });
        observer.observe(solutionList, { childList: true, subtree: true });
    }

Neither BackgroundCheck.refresh() or BackgroundCheck.refresh(target) add the needed classes to the targets. Instead I get Uncaught [object HTMLHeadingElement] is not a target in the console.