This type of problem typically occurs when you are running the incorrect PHP version.
I see that you have indicated in your original post that you are running PHP 7.2, however would you mind double checking that? If you can post the output of php -v or a screenshot of Mautic > Configuration > System Info page, it would help.
This is from a different repo (not Mautic), but somebody was encountering an error with the same file as you vendor/aws/aws-sdk-php/src/functions.php when they were running a PHP version that was too old.
So as an update, I installed Mautic on a brand new Ubuntu (instead of CentOS) VPS. The chron jobs run just fine on this Ubuntu VPS, however it would be nice to know why it won’t run on the otherwise vanilla CentOS VPS…