I have seen reports on other threads that when people enabled Telstra air their speed dropped to non-speed boost speeds (30-36Mbps), yet when they turned it off speeds returned to normal.
https://crowdsupport.telstra.com.au/t5/Telstra-Air/Activating-Telstra-Air-slows-home-wifi-a-lot/m-p/490668#M683
I would let the technician come out and rule out any hardware related issues, but also see what happens if you disable Telstra Air in My Account and the modem.
https://crowdsupport.telstra.com.au/t5/Telstra-Air/Activating-Telstra-Air-slows-home-wifi-a-lot/m-p/490668#M683
I would let the technician come out and rule out any hardware related issues, but also see what happens if you disable Telstra Air in My Account and the modem.