That is due to a change I have made to ensure the collapsible sections panel is always last. The code does:

function handleSidePanelChanges() {
    const sidePanel = document.getElementById("side-panel");
    const collapsePanel = sidePanel.children.namedItem("console-section-container");

    // Move the collapsible section headers to the last position
    if (sidePanel.lastElementChild !== collapsePanel) {
        sidePanel.lastElementChild.after(collapsePanel);
    }
}

new MutationObserver(handleSidePanelChanges)
    .observe(document.getElementById("side-panel"), { childList: true });

When the side-panel childs change, if the console-section-container child is not the last one, it is moved to be after the last child. That in turns trigger the observer and the code runs again. Looks like that does not quite work :/

I have found it. I have not tested it when there is no collapsible section. When the timestamper plugin adds its panel to the sidebar that triggers the observer, namedItem('console-section-container') returns null and never fulfills the condition that the last element is console-section-container. The code should abort early when the panel does not exist (`if (collapsePanel === null) return;).

Mentioned in SAL (#wikimedia-releng) [2024-11-04T11:42:47Z] <hashar> Restarted CI Jenkins to update the Collapsible Sections plugin due to T378864 # T378327

Thank you for the quick fix!