I found this thread which has the same issue as me but just wondered if there was any update on the issue being fixed? i have tried this on custom post types and user (custom tables) and I cannot return a value. It only works for values which exist in the default postmeta and usermeta tables.
Ok so I am running this code inside a class within my own plugin (oop structure). I have just realised this is being called too early? If i wrap this code inside wp_loaded it works. I guess I cant use the helper function then as I need this to run before the page loads. Is there any other option? other than direct wpbd calls?