When launching SketchUp Pro 2017, I get a message: SkethUp Update Service | A new version of SketchUp is available. | Download Now". However, I get a “404 | Stranded? There’s another way out.” error.
What is the version number of your SketchUp 2017 installation?
The latest version can be downloaded here
That would already be the last version of SU2017. I expect it’s suggesting to you that SU2018 is available. Why the link doesn’t work, I don’t know. But you can download it from the link I provided earlier.