wp-cli commands do nothing, return nothing

I’m using wp-cli 1.5.1. My server is running php7.2.

I’m not running suhosin.
(Some people seem to think that suhosin may cause the same symptom)

When I issue wpcli commands within a non-wordpress directory I get the expected outcome: and error message saying “This does not seem to be a WordPress install.”

However, when I run wpcli commands within wordpress directories,the prompt returns quickly without output.

This seems to apply to most variations of ‘wpcli plugin’, ‘wpcli theme’, ‘wpci search-replace’ and ‘wp theme’. These are the ones that I’ve tested.

‘wp –version’ and ‘wp –help’ return the expected output’.

What could be happening here?