Hi jj-hannas,
Please try whitelisting the following URL's:
ccmdl.adobe.com:80
swupmf.adobe.com:80
swupdl.adobe.com:80
https://na1mbls.licenses.adobe.com
https://ims-na1.adobelogin.com
https://adobeid-na1.services.adobe.com
https://na1r.services.adobe.com
ccmdls.adobe.com:443
ims-na1.adobelogin.com:443
na1r.services.adobe.com:443
prod-rel-ffc-ccm.oobesaas.adobe.com:443
lm.licenses.adobe.com:443
www-du1.adobe.com
If still you get error while signing in then I would suggest you to create a full installation package on a open network and then deploy it on user machine.
Regards,
Romit Sinha