Vivaldi 2.5 stuck on loading WhatsApp Web

Today i upgraded vivaldi-stable (2.4.1488.38-1) to 2.5.1525.40-1.
After it i was no longer able to load WhatsApp Web.
Only got the Notification „WhatsApp works with Google Chrome 36+“ shown below.

Perhaps WhatsApp isn’t able to read the HTTP Request Headers -> „User-Agent“ correct. Or the developers are not a friend of Vivaldi ^^
In my case that’s:

Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/74.0.3729.134 Safari/537.36 Vivaldi/2.5.1525.40

As possible workaround i decided to use the Chrome Extension „Modify Header Value (HTTP Headers)“ to changed the User-Agent. The Vivaldi Extensions can be viewed within: „vivaldi://extensions„

After installing the extension add the following rule.
The configuration page can be opened via the small globe icon within the navigation bar -> I. Open options page,
or throuh the „vivaldi://extensions“ site -> click on „Details“ in tile „Modify Header Value (HTTP Headers), after that -> „extensionoptions“

URL: https://web.whatsapp.com/*
Domain: yes
Sub: yes
Header Name: User-Agent
Add: no
Modify: yes
Remove: no
Header Valuke: "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/74.0.3729.131 Safari/537.36"
[Without quotation marks]
#click on + "Add Header Item"

From now Vivaldi sends a modified User-Agent for the Site: web.whtasapp.com
After that you should be able the access WhatsApp Web again.