For customers experiencing any issues with their NBN service, we recommend the best thing to do first is check if there's an outage on the NBN network.
We have created this article that can guide you on How to Check for NBN Network Outage
If there are no known outages in your area, customers can proceed with the troubleshooting steps indicated on this link : https://www.tpg.com.au/support/nbn-hfc-cable/problems_speed_nbn_hfc
We've also created an article that will guide you with some troubleshooting steps for Slow speed issue.
You may also perform a reset with your NBN NTD box and the TPG supplied modem/router, before performing the troubleshooting in order to start fresh.
(note: the modem/router will go back to it's default settings once you've done a reset.)
Feel free to search Community for help with your issue, or contact us and we'd be glad to assist you.