In multiple different versions of Visual Studio (2010-2017) the toolbox tend to disappear in designer mode when working on SSIS packages. Select “SSIS” then “SSIS ToolBox”

It should look like the following when the toolbox is added.

In Visual Studio 2019 the same problem occurs. The toolbox tend to disappear and can be added using the following steps. Select “Extensions” >> “SSIS”>>”SSIS Toolbox”.

Once the toolbox is added it should look like the following.