Hi @qstudio
It is possible that you have a large amount of posts in the DB, and because the current post_object field is not efficient, it is failing to query all the pages form the DB.
This has been fixed in ACF5 (soon to be released), but it may also be another issue entirely.
You said that the issue only happens on the live site, not local? This points to the issue being a DB load problem.
If you want, I can log into your site, and if you give me access to edit plugins, I can do some debugging in the post_object field to find the issue?
Thanks
E
