Welcome to TPG Community!
We were able to locate your account and learned that you've contacted our Tech team yesterday and the case was escalated to our Engineering team.
After further investigation, our Engineering team contacted you and was informed that the issue of the dropouts was caused by the over utilization of the upload bandwidth, since you are under our basic NBN12/1 speed tier plan. I understand that they've advised you to upgrade to the next plan which is the NBN50 speed tier with a typical evening speed of 44.5 Mbps.
The changes were already applied today and we can see that the modem is getting a good sync speed of 54 Mbps Downstream and 22 Mbps Upstream.
Please observe your connection further and advised us if the issue still persist.