Hi @noisemedia
Thanks for the question.
You will find the same issue in this thread:
http://support.advancedcustomfields.com/forums/topic/option-fields-not-saving-within-flexible-content/
In short:
The wp_options table has a character limit of 64 on the options_name column. This means that WP can’t save any data that exceeds this limit. Your nested repeater field is most likely causing the field_name to become too long.
Please read the linked thread for some solutions.
Thanks
E