As I said before, it does look like a memory limit issue, however I’m not seeing any debug message with the usual “Allowed memory size of xxx bytes exhausted”.
I tried increasing memory limit via php.ini, htaccess, wp-config.php with no joy.
Funny thing is that if I use a relationship field instead of post object or page link, it works fine (and that’s how I solved the issue for the time being…).
Thanks again Elliot for your support