After troubleshooting an issue with SharePoint Designer, I wanted to document the fix for others. Installing the “DP.CustomActions” WSP from CodePlex worked well on SharePoint 2010 and 2013. However, with 2016 an issue occurs which requires additional [web.config] modification. Details below. Cheers!

Issue
- WSP is fully deployed and installed
- Custom Action workflow steps are visible in SharePoint Designer
- Click action then suggestion menu disappears. No action sentence is visible on designer.
Resolution
- Locate </targetFx> in [web.config] file
- Add below XML code both before AND after </targetFx>
<authorizedType Assembly=”DP.Sharepoint.Workflow, Version=1.0.0.0, Culture=neutral, PublicKeyToken=0298457208daed83″ Namespace=”DP.Sharepoint.Workflow” TypeName=”*” Authorized=”True” />
- IISRESET
- Clear SharePoint Designer client cache https://stackoverflow.com/questions/43113666/how-to-clear-cache-in-sharepoint-designer-site
- Test
Root Cause
- Appears that SharePoint 2016 leverages more Dot Net Framework versions (3.0, 3.5, 4.0, 4.5) and has a larger [web.config] to support backward compatibility with multiple Dot Net versions.