I am currently unable to download and import files from 3D warehouse into sketchupWeb.
Also, I can’t find any of my last projects. All of these projects were saved only online. Is there any chance I can recover these projects?
In 99% of the cases, this is because you did not use the same email address to log in as the one you used when you made the above models/projects.
Try to Log out and log in with your original user credentials.
However using 3D warehouse should not inflected, unless you want to use your private models uploaded with your original user credentials.