Starting mid-October 2015, you may see a significant drop in “conversions”. With the new change from, Google, the conversion column will only display the conversions that have “Optimization” selected. This supplemental customization will let you prioritize the conversion actions that are most significant for your business.
You may now be able to see that the “Conv. (opt.)” column will be removed since its data will now appear in the updated “Conversions” column. These changes will give authority to the advertisers to bid to new conversion types and attribution models, two of the priority areas which are based on customer insights and feedback.
These controls and new conversion types are not offered for the “Converted clicks” column. The overall goal of this change from AdWords was to make it more spontaneous, as this gives more control over the data. For more information, you can see the Google+ post and support article.AdWords To Report Only Optimized Conversions For Reporting & Columns!,