Since November Opera VPN was not working for me. I finally found a culprit. I have a Asus router with AiProtection that uses Trend Micro service. When VPN is turned on, it contacts https://api.sec-tunnel.com/ and other addresses from the same domain and it it blocked by Trend Micro. They have it categorized in "Proxy Avoidance and Anonymizers" which they consider as malicious. So the only solution is to turn off Malicious Sites Blocking in AiProtection. Of course, better solution would be to reconsider addresses from sec-tunnel.com as safe. You can report it at https://global.sitesafety.trendmicro.com/. I did.