Please can you log into your Asus router and check what 'WAN Connection Type' is currently configured?
See attached picture.
I suspect it will either be 'Automatic IP', or more likely 'PPPoE' where you also had to specify your plusnet username & password.
'PPPoE' option on Asus will not work with the Hub One, because the Hub One does not offer a 'bridge modem' mode. If you want to use PPPoE, you will need a VDSL modem such as the ones provided by Openreach.
ex-Plusnet (ADSL, FTTC) 2008-2023. now BT (FTTP) 2023-