We developed a new website for our company. 
The old website work on Joomla 2.5, for example **https**://www.company.com.
Page www.company.com/administrator closed by password via .htaccess

The new website we developed on Joomla 3.9, placed it on a temporary separate domain, for example **http**://www.test.com.
This website disallowed for indexing by robots.txt.
Page www.test.com/administrator is available without a password .htaccess.
Https version is available only via self-signed certificate.
The new website is radically different design.

After a month of development, when the website is almost ready there was a problem.
Website www.test.com has been blocked by Google Safe Browsing.
[![Warning - Deceptive site ahead](https://i.stack.imgur.com/ETAUk.png)](https://i.stack.imgur.com/ETAUk.png)
The website is blocked in Chrome, Firefox, Safari.

Google Search Console Screenshots :
[![Search Console 1](https://i.stack.imgur.com/HwFNI.png)](https://i.stack.imgur.com/HwFNI.png)
[![Search Console 2](https://i.stack.imgur.com/Iz7ej.png)](https://i.stack.imgur.com/Iz7ej.png)

I checked the page www.test.com/administrator for viruses 
[![scan - sucuri](https://i.stack.imgur.com/2glDQ.png)](https://i.stack.imgur.com/2glDQ.png)
I compared the files with standard files of Joomla. There is no difference, all files is okey.
Didn't find anything suspicious.

I checked on virustotal
[![scan - virustotal](https://i.stack.imgur.com/fHe4T.png)](https://i.stack.imgur.com/fHe4T.png)

I can't find the true cause.

* The message in the browser: Deceptive website ahead
* The message in Google Search Console: Harmful content
* The message in Virustotal (Google Safebrowsing): Phishing

I am afraid to upload the new website to the main domain.

Can the new website be blacklisted on the primary domain?

How to determine the exact cause for blocking?

Is the default page for Joomla /administrator has security problems, and google blocks the whole website?