I set input vars to 10000 (I even tried 20000) and still could not add more than 30 custom fields to a field group. To continue, I had to create a new custom field group and split the fields out which is not ideal.
I am using a powerful dedicated server so this is not a resources issue but instead seams to be a limitation of Metabox.
Lagging when adding too many fields (I need 40)! Cannot drag/reorder any field because it's too slow. And finally crashed the whole site, could not change or even update field group location in the field group settings...it does not want to update this field anymore and I am locked to 'archive' and cannot even entera prefix (it takes 30 seconds to display it). Also the json exported is not correct and had to modifiy it for missing }}] and so on. I ahd to delete all fields, import and use old metabox versions to make sure, if making sure of anything is the right word.
Increasing the php max_input_vars to 10k did the job.
Problem seems to be fixed, not for the bad json export file that is still missing closing tags nor the huge lag when trying to drag/drop and reorder fields elements. At least it's not crashing field groups settings anymore.
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