I have installed the Data-Tier Application Framework and SQL Server Data Tools for VS 2017 . I created a solution then returned to it a week later and the SSIS toolbox had disappeared.
I opened the toolbox window using View -> Toolbox but it was empty.
To get the SSIS toolbox back, right-click on the SSIS design surface in the project and select SSIS Toolbox – hey presto! it reappears.