When editing a CUSTOMIZED FIELD, in the SETTINGS tab, the POST location, when changing to display the fields in another POST TYPE, after saving, does not save the change and always returns to the POST location. This error occurs in old custom fields after some change. Apparently the new ones don't have this problem.
Can you try editing settings for any field and see if it can be saved? If not, then I think the problem is the number of inputs exceed the PHP limit. If that's the case, please see the solution here:
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