It happens from time to time that the number of custom fields is temporary stuck. This can be avoided by increasing the amount of memory_limit and other parameters in the php.ini
I just tried this way today, but my number of custom fields remains stuck at a certain level. Is there another things to deal with to increase the possible amount of custom fields in the metabox Edit Field Group?
Thank again Long for your valuable help!
It worked when I determined the max number of input variables of the project, inserting: php_value max_input_vars 10000
in the <Ifmodule> tags of the .htaccess file of my project.