I got that behaviour too prior to 24 August 2017 at my area i.e. Bukit Jalil, for peak hours 7 PM - 1 AM. Speed often dropped below 1 Mbps even and only 1 web related activity can be done at any time

The above was fixed somewhat after said date above. Likely they did some maintenance to alleviate congestion in my area. It's not as fast as recorded by some lucky folks here, but not infuriatingly slow like it was before. Also can open multiple tabs now without the connection coming to a halt

That's usual with LTE network. It's known as buffer bloat.

You can fix it by limiting your speed so the experience can be better.