wpephpcompat_start_test_cron shows but no output

WP 4.9.6. PHP 5.6. Installed PHP Compatibility checker. Installed WP Control (https://www.ads-software.com/plugins/wp-crontrol/).

After first selecting PHP 7.2 radio button, then hitting “Start scan” button in PHP Compatibility checker, the process widget goes round and round.

After a while i got an “Error: Status: 500” popup, clicked OK. Process widget still going round and round.

Looked at Tools->Cron Events and see this:
wpephpcompat_start_test_cron None WPEngine_PHPCompat->start_test() 2018-06-28 23:05:16 (41 seconds)

And then i refresh page and it has counted down time till run. When it goes below 0 or Now, it is queued up again at around 1 minute to go. This keeps repeating. No output.

Any clues?

How to restart?

Thoughts?

Peace,
Dan