It could be a plugin malfunctioning and allowing the restricted users to delete posts. It could also be an early sign of the site having been hacked. I would suggest testing your site with a plugin like WordFence to see if it has been compromised. If WordFence returns a clean report then contact the author of the plugin you use to restrict those other users because it is likely the plugin malfunctioning!
Hope this helps.
Now i am having Another issue after restore the Backup errr[The site is experiencing technical difficulties. Please check your site admin email inbox for instructions.]
Check your email for further instructions.
Update :
Cause: Updating Plugins in More than one at the same time. Posts are getting Deleted. Except Pages And Trash Posts
Still I am not aware of how to fix this issue