TypeError: Failed to execute 'observe' on 'ResizeObserver': parameter 1 is not of type 'Element'. in `monitorResize`

util.js の monitorResize から始め、Align.js:110 からの呼び出しを調べます。issue に記載されたホバー操作を再現し、ResizeObserver.observe にどの値が渡されるかを確認します。完了条件は、ホバー経路で報告された TypeError が発生しなくなることです。issue ではテストファイルは指定されていません。

The following error happens when hovering an element.

See video: https://youtu.be/-aLHvTHvp7Q

TypeError: Failed to execute 'observe' on 'ResizeObserver': parameter 1 is not of type 'Element'.
    at ft (util.js:58)
    at Align.js:110
    at Oi (react-dom.production.min.js:262)
    at KqkS.t.unstable_runWithPriority (scheduler.production.min.js:18)
    at jl (react-dom.production.min.js:122)
    at Ti (react-dom.production.min.js:261)
    at pi (react-dom.production.min.js:243)
    at react-dom.production.min.js:123
    at KqkS.t.unstable_runWithPriority (scheduler.production.min.js:18)
    at jl (react-dom.production.min.js:122)
    at Hl (react-dom.production.min.js:123)
    at $l (react-dom.production.min.js:122)
    at De (react-dom.production.min.js:292)
    at react-dom.production.min.js:50
    at zr (react-dom.production.min.js:105)
    at Zt (react-dom.production.min.js:75)
    at Jt (react-dom.production.min.js:74)
    at KqkS.t.unstable_runWithPriority (scheduler.production.min.js:18)
    at Gt (react-dom.production.min.js:73)
    at HTMLDivElement.o (helpers.js:72)

Unminified code monitorResize:

export function monitorResize(element, callback) {
    var prevWidth = null;
    var prevHeight = null;

    function onResize(_ref) {
        var _ref2 = _slicedToArray(_ref, 1)
          , target = _ref2[0].target;

        if (!document.documentElement.contains(target))
            return;

        var _target$getBoundingCl = target.getBoundingClientRect()
          , width = _target$getBoundingCl.width
          , height = _target$getBoundingCl.height;

        var fixedWidth = Math.floor(width);
        var fixedHeight = Math.floor(height);

        if (prevWidth !== fixedWidth || prevHeight !== fixedHeight) {
            // https://webkit.org/blog/9997/resizeobserver-in-webkit/
            Promise.resolve().then(function() {
                callback({
                    width: fixedWidth,
                    height: fixedHeight
                });
            });
        }

        prevWidth = fixedWidth;
        prevHeight = fixedHeight;
    }

    var resizeObserver = new ResizeObserver(onResize);

    if (element) {
        resizeObserver.observe(element); // CRASHES HERE
    }

    return function() {
        resizeObserver.disconnect();
    }
    ;
}