Low download-speed after upgrade to LEAP 42.3

I’ve been running LEAP 42.2 KDE for å long time. I never had any problem with network-speed. Our company have a fiber-connection 300/300.
Now i upgraded to LEAP 42.3 KDE. When i test network-speed using http://speedtest.net i now only get 35 down and 280 up. I run this several times and get the same result.
At de same time i run Virtualbox and Windows 10 as guest-OS. Network is bridge trough the same NIC. If i meassure network-speed in Win10, i get 260/260. This is normal. Its not my network cable that is bad.

Then i did a test. I tried different web-browser: Vivaldi 1.15.1147.42(based on Google) and Chrome 66.0.3359.181 i get the same result (aprox 35/280), but if i try Mozilla Firefox ESR 52.8.0 then i get 280/280.
All browsers are reported running Flash 29,0,0,171

Then i was thinking maybe there is something with the Flash-implementation for Google and Google-based browsers?

Anyone that experience similar issues?