@Sunshine 

Hello,

Thank you for the answer.

I don't experience any disconnection of the internet connection during WiFi calling or general use.

The problem seems to be related to WiFi calling, people who have similar problems in the forum have usually solved it by updating their modem / network extender, but my devices are up to date.

There are users who have solved the problem by changing some settings in the advanced options, I tried it myself but the result was the same.

Also, as you mentioned, the LED lights on my RE600x were solid and blue.

In the connection settings on my phone, I found an option to prioritize the wifi call and chose that option, unfortunately the problem is the same: the call starts normally and stops after about 1 minute. Meanwhile, there is no interruption in my internet connection.

The RE600x is connected wirelessly to my main router with no other connection devices in between. If you are talking about a wired connection, I can't do that because the modem (my main router) is upstairs and the Re600x is downstairs, which is why I bought the Re600x.

  @Sunshine

Has anyone actuall solved this issue yet?

My RE600X does the same. There are no issues with the extender and it's Internet connection other than the fact the wifi calling doesn't work properly. It always drops out after around 1 minute. Please note that if I connect to my normal router, then wifi calling works perfectly fine. 

It's really disappointing as the only reason I bought th extender was so that I could use wifi calling throughout my home, as the wifi from the router isn't strong enough to reach certain areas in the house.