Presumably you mean you are now on FTTP (full fibre). After continual dropouts on FTTN caused by dodgy copper joints, I made the step to full fibre, and my dropouts have ceased completely. . If it is FTTP then is the Optical light on the NTD flashing? If so, assuming you have removed the DSL connection and linked the NTD with WAN, data is coming through that far. I suspect some part of your installation is to blame. I would first look at connecting leads (Cat 6) and fully plugged in rj45s. Then I would suspect the router.
Did you notice any changes with the light status of the NBN NTD box and router when the connection drops out?
Do you experience the dropouts on devices connected to both WiFi and Wired?
What troubleshooting have you tried so far?