After trying absolutely everything to fix this issue and enduring material interruption to my business to find any solution, TPG has failed to deliver a connection that works. We have been going round in circles for months now, having tried multiple routers, 2 NBN visits confirming their infrastructure is fine, indepdent technicians confirm all is working other than TPG service. We have had no choice but to end the contract for failure to deliver the service, however TPG has had the audacity to charge an early termination fee of $350 - I am absolutely disgusted at the behaviour and will be taking further. If anyone has had a similar experience I'd love to hear more about it.
Just closing this out. After the absolute nightmare we had with TPG we switched servive providers and instantly the problem was resolved and we have had no more issues since. So despite a huge amount of wasted time and never really getting to the bottom of what was happening, it is clear the issue was on TPG's end.