by Ken Task.
Thought ... Check settings for max_input_vars via Admin Server PHPinfo.
https://moodledev.io/general/releases/4.5
PHP setting max_input_vars must be >= 5000. For further details, see Environment - max input vars.
If it is already the minimum of 5000 increase to 6000 and restart apache/web service.
Setting is sensitive to the operations you are trying to perform: backup/restore of a course, large quiz banks.
'SoS', Ken