Thumbnail showing in very small size

I am using this plugin from a long time. Few days ago thumbnails on my site Howtoconnect – Windows 8, Apps, Android, Internet, Computer tips got very small. I am puzzled. I run Auto Post Thumbnail 2 times to improve the result, but in vain. I am trying everything from my part. Please solve my problem.

https://wordpress.org/plugins/auto-post-thumbnail/