I'm in! the Telstra Optimiser is now working. Unless someone else did something remotely the key appears to be;
Deactivate Internet Optimiser using the My Telstra app
Factory reset of modem
Reactivate Internet Optimiser in the My Telstra app
Clear cache in browser.
I had cleared the cache previously but not in the sequence above.
Thank you @Netduma Fraser and @MuRF FuRY for your assistance.
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Butts got a reaction from Mr MuRFiE in Please wait until Telstra Optimiser has fully loaded message