I need some information to asess your no sync issue.
where modem is connected?
how's socket and cable condition?
how many socket you have in house?
which light are ON for router?
make sure socket is connected to DSL port of router.
TPG provide differnt plan, customer choose their plan based on their requirement, Your plan is nbn50 so based on that speed is 50 Mbps for download and 20 Mbps for upload. Sync speed is actually unit which measure speed of internet connection. FYI I have also noted that if you want to upgrade plan then nbn 100 speed is also available for you FTTN connection, not all FTTN customer can get this nbn100 speed due to distance from node but your house is closer to node so nbn100 speed is avaialable.
I hope this information can help.