Sudden inability to run a PHP Cron

Hi,

we’ve had Crontrol running for years now without any problem, on a live site and on a test site.

There is one PHP Cron Job executing wp_remote_get(“myurl”), and it stopped working a few days ago. I have no Idea why. Nobody has changed anything. I managed to run once or twice by hand, using the “run now” command, but now this always fails. The cron job is placed on top of the queue and it says “next run: 1970-01-01 01:00:01” (?). Then it is placed at the bottom of the queue and rescheduled (like it should be).

I checked the plugin page in our WP backend, and it says in red “Error: This Plugin needs a newer version of WordPress. Click here to update”.
Our WP version is 5.3.16, has been like that for years. The Crontrol detail page says whe have V 1.16.2, which is weird, because nobody has made any updates. The source code of wp-crontrol-php says “Version: 1.8.5”, and the file is from 2020. So we obviously have 1.8.5. which runs well with WP 5.3.16, and this cannot be the reason of the cron job failing.

So, the error must be something else. But what? Is there some kind of error log or other way to see what happend?