Update 22/5/2019 : The bug is resolved. Users can surf at full speed.
Is this coincidental . TPG does that for it’s trial plan. giga! which was launched 2 days ago seems to have this strange bug. After running the network with tests exceeding 2 GB of data, the network speed seems to be throttled down to 1.5 Mbps.
Changing the APN from giga to starhub shwap does not help. It is not sure if this is a bug or is meant to be so.
You can read about it here.