Regression: Template Composer: Can't open component property box (first time with clean browser)

Sometimes, the component property boxes can't be opened. So in the Template Composer, click on "Edit template", then click a component to try to open the properties box.

To reproduce (in Go Green):

• Open a completely fresh browser (e.g. incognito mode in Chrome will do)
• Go to the CMS
• Go to the Channel Manager and open a channel
• Click "Edit template"
• Click a component
  Expected: Component property box opens.
  Actual: A Javascript warning is issued. See below.
  Workaround: refresh the browser.

Javascript warining:
Handling onClick for element[id=cb756d48-f8fd-402f-a0c1-f64079439961] with no record in component store page-editor-all.js:1511
Which is here:
record = this.pageContext.stores.pageModel.getById(id);
if (!record) {
console.warn('Handling onClick for element[id=' + id + '] with no record in component store');
return;
}