This is due to a new setting added to SXA in 1.8 that has a known bug.
The setting is XA.Foundation.Theming.AssetsOptimizationSwitch.Enabled, it is disabled by default so that users cannot disable the asset optimizer on the CD servers.
As a work around, for now you can re-enable the asset optimizer switch and also disable the asset optimizer for your site. ...
The Creative Exchange Import process deletes the gulpfile.babel.js (since a dot is not a valid character for the item name).
From Sitecore support I got the tip to rename the 'gulpfilebabel'-item to 'gulpfile' and change the extension from 'js' to 'babel.js'. And that works for me, the item was not deleted anymore.
Solved this by using
in every file upload/delete post/get because I'm using a self-signed certificate.
I changed the following files in the gulp\util folder inside the theme root folder:
search for 'url: url' and add to the request get/post call the parameter '...
This happens because when the Creative Exchange exports the theme files, it exports the gulpfile.babel.js file without the . between gulpfile and babel. A period is normally an invalid character for an item name, so that was probably stripped when the file was added.
If you rename the file to have the period back in (gulpfile.babel.js), gulp will then be ...