Insert page not including content any more

<!–

[Insert-page ] stopped inserting content at some point.

After some amount of messing around, I found that if I created a new WP page and copied (copy/paste) the content from what I’ll call the “original master page” (including the insert-page statement) to the new page then the inserted page content appeared when I accessed the new page.

I wondered if this was a caching issue.

So:
1. cleared the local cache: NG
2. tried publishing a small change to the original “master” page: change appeared ok;

I’m certainly just an amateur with respect to WP so I could be missing something obvious.

WordPress 4.9.20 running Tempera theme.

Any ideas ?

Thanks

Bill Meier

—–
/* page inspection when fetching the original master page (extract)
https://www.hackensackriverkeeper.org/activities-and-events/eco-cruises-1/
*/

<h3>2022 Eco-Cruise Schedule<br />
</h3>

<div data-post-id=’3540′ class=’insert-page insert-page-3540 ‘></div>

<!– no content appears –>
——-
/* page inspection when fetching the copied master page
https://www.hackensackriverkeeper.org/activities-and-events/ecocruisetest/
*/
<h3>2022 Eco-Cruise Schedule<br />
</h3>

<div data-post-id=’3540′ class=’insert-page insert-page-3540 ‘><div id=”fb-root”></div>
<!– The content –>
<div>
<div style=”float: left; width: 33%;”>
<p>APRIL<br />

–>