Could not update post in the database

I have been using WordPress on a client’s blog from past 6 years and it has been working fine. I am trying to update a post to remove some broken links and it is not allowing me to update the posts by removing the links. This is a really weird stuff as the same link was linked in multiple posts. Out of 20 posts, I was able to remove them from around 14-15 posts but not from the remaining 6 posts. I have gone through posts here and here but none of the solution is working for me. Can you please advise on what can be done to resolve this.

I am sure this is not a WordPress Version isssue as I had this issue on 4.5.3 as well.

Looking for a response.