It's not resolved for me I'm afraid. It's the same on multiple devices, browsers and websites using the Virgin mobile SIM.
E.g. do a search for national lottery, click the link for national lottery website or any other similar site such as postcode lottery. I receive a message "This site can't provide a secure connection". All of the search results links use HTTPS.
I've searched the community and found people having similar problems in the past where your technical team had to manually disable parental controls. It was already disabled in the VM control panel and I've tried turning it on and off again as well as restarting devices.
If I use a VPN or a built in data saving facility such as in the Opera web browser then it works fine. It's just if going directly through VM all such sites refuse to load.