Hi
A quick update, I am still having this same login problem.
I am now running Linux Mint 20.1, Wine 6.0, and a fresh installation of Sketchup 2017 Make (64b).
Using the Sketchucation 4.0.0 plugin the button to "Not a member? Register" works correctly, but the "Sign in" button with Sketchucation credentials fails with a message: "Some error occured please contact the administrator at sketcucation.com"
I hope someone can shed light on this problem. I can use the same credentials in a browser to login to Sketchucation, but logging in from inside Sketchup 2017 Make repeatedly fails.
Thank you,
...Patrick