That looks like the post meta data for a post (possibly one that has been deleted) has been corrupted in your database. A WordPress database ‘cleanup’ tool might remove it. Essentially, there are two tables in the database that are connected to this.
The posts table and the post meta table.
Each entry in the post meta table has a post ID to link it to. What I think must have have happened is that there will be an entry in the Post Meta table where the Post ID stored no longer exists in the Posts table. Whilst I have not used a cleanup plugin for some time, I think there will be a plugin that looks for those ‘lost’ records and deletes them.
OR, the actual data in a valid post meta table entry has become corrupt. I do not know which it is. It would not be hard to find using a plugin like ARI Adminer (which is how I now do it when I have a database issue).