Most of the time a user don't have permission to use the input filter assign to that node this changes can be made by an administrator or any person who has access for input filter permission which leads to the user never had, or no longer has permission to use the input filter associated with the node. So in that case you need to restore permission for the user to access the filter used when the content was first created by him for that you need to run an sql query which would be as follows
Code:
SELECT n_id, u_id, title1, format FROM {node_revisions} WHERE format <> {default_filter_id} AND u_id <> 1;
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