Update:
I am able to resolve the issue by publishing the new post (with new URL). I was lucky that it didn’t happen to all my URLs. Only one URL was effected therefore, I removed that infected one. Still unable to determine the root cause of the problem.
Thanks Samuel for the prompt reply but it was an auto generated URL according to the title of the post. Now I have tried to edit it manually but first after the post is updated no change in URL takes place. Second, problem is that if I simply put URL with ef bb marks, it leads me to 404 page. The third point is that if I paste this complete spoiled URL in a browser, it redirects me to the original one.
