I was still having this issue, even with version 3.13.1 of the SSIS extension, so I posted the question on marketplace (here) and got this temporary workaround:
- Click “Edit Script” to open VS
- Right click on the project, and click “Open Folder in File Explorer”
- Open the proj file in some text editor
- Modify two “<OutputPath>bin\</OutputPath>” elements to “<OutputPath>.\bin\</OutputPath>”, or simply delete the two OutputPath elements
- Save the proj file, and now you can try to rebuild the project in VS.
Works for me, deleting the 2 OutputPaths was easiest.
Aidan