I been battling with this weird issue for 3 days.
The thing is that after creating 55 fields of different kinds (text, text areas, tabs, repeaters) when adding an extra field it just doesn't show on the back-end nor on the front-end (but it seems it is written on the DB, as I see those new rows on the post_meta table)
I've tried creating new field groups and starting it over all again, but still having the same problem, I noticed it happens after duplicating many fields.
I'm not sure what's the nature of this problem...hope you have some clue about it.
Adding this to my php configuration file solved it!
suhosin.post.max_vars = 20000
suhosin.request.max_vars = 20000