Welcome to the community !
It is possible that the dropout/packet loss you experience on 5Ghz WiFI connection is caused by Wireless Interference.
By default the 5Ghz Channel and Bandwidth are set to “Auto”. These settings were changed by specifying a channel and setting Bandwidth to 40MHz.
It is best to use a WiFi analyser to scan the 5GHz frequency to select a channel that has no or minimal interference when making the changes.
There are free WiFi analyser application available on Apple Store/Google Play Store that you can install and use to check which Wi-Fi channel have less interference.
We'd like to set your expectation that TPG is not promoting any specific application nor will it be responsible for any possible issue that it may cause on the system.
We also did an article that you may find helpful, please see link below.
I've got exactly the same problem as mentioned above.
The same router, working fine on 2.4GHz and loosing packets on 5GHz.
Tried factory reset, no luck.
Can you help me here? Thanks