I had the same problem and it had me perplexed for a while. My Command Line Interface script bootstraps ProcessWire and then fails without even the tiniest hint of an error message.
In my case, the problem was that code from /site/ready.php was being executed when ProcessWire was bootstrapped. The code I had in /site/ready.php was only intended for execution in specific situations while web browsing (not CLI). So I took the code inside that file and wrapped it inside this:
if(php_sapi_name() !== "cli") {
// code inside /site/ready.php
}
