Final I found the solution.

Replace the Base URL from `` to `//`

CAUTION! The change is not allowed in magento2 admin.

I made it in MySQL in table cron_config_data and record with path='web/unsecure/base_url'. After cache:clean and varnish restart everything works smoothly in frontend.

Unfortunately problem remains in Backend. Magento2 redirects to this url: ``

This last problem solved by simply change the Admin base url from Stores -> Configuration -> Advanced -> Admin -> Custom Admin URL = ``