Hi @thestart,
Thanks for the post.
It is possible that your server is terminating the save process before ACF can finish the field’s save process.
Please increase your max_vars setting by making the following changes to your php.ini file:
max_input_vars = 3000
suhosin.get.max_vars = 3000
suhosin.post.max_vars = 3000
suhosin.request.max_vars = 3000