When I’m on Wi-Fi, everything works.
When I’m on mobile (Celcom), my browser (usually Chrome, but I’ve tried others) always gets a time-out when accessing anything that uses HTTPS.
Non-HTTPS sites are fine.
This means, for example, that I can’t do a Google search when I’m on the mobile network – it always fails.

This started happening a few weeks ago, and happens 99% of the time. I don’t think I’ve changed anything that would affect it – as it is only a problem on mobile (not Wi-Fi), and affects all the browsers I’ve tried, it feels more like a network problem than a phone problem.