We’re running into a strange issue where field groups with one ore more Flexible content fields stop saving updates when the total number of layouts among those flexible content fields reaches 34 or so. One group broke at 30 layouts + 4 tabs (don’t know if that’s coincidental or not), one at 34.
What I mean when I say it stops saving updates is that you can’t add new fields to that group, and if you change one of the rules or options (Show only on posts, or Position = Side) and then click update, those changes are not saved. The fields themselves (on the edit post page) save the content added to them, we just can’t modify the field group.
We are running WP 3.6, ACF 4.2.0 and Flexible Content Field 1.0.2