Updating wpephpcompat_start_test_cron Didn’t Unstick Scan

I set up a staging site for the site listed above to test a new theme. The reason for putting a new theme on the site because the current theme is apparently incompatible with recent versions of PHP. I selected a new theme in the staging site and have been trying to run PHP Compatibility Checker which, so far, has hung every time I’ve tried to run it. Checking the FAQ for the plugin, I found the following:

The scan is stuck, what can I do?
The PHP Compatibility Checker relies on WP-Cron to process plugins/themes in batches, this is necessary to avoid server timeouts. The scan will get stuck if your site’s WP-Cron isn’t functioning. You can look into this using WP Crontrol. The cron is called wpephpcompat_start_test_cron. This could also be an issue if your site is using basic authentication.

In reviewing wpephpcompat_start_test_cron in the staging site’s administrative dashboard, I found the cron was apparently not scheduled to run, so I set it to run weekly and had another go at running PHP Compatibility Checker. Still stuck. What am I doing wrong? Thanks for any advice!

The page I need help with: [log in to see the link]