asus RT-AC5300 in repeater mode cant see my network

hi. i have an asus RT-AC5300 i use as a repeater to connect to my shaw fibre+ gateway router. recently my old gateway broke and was replaced, and ever since my asus router can only see the 2.4 ghz network that i have, and not the 5ghz network i used to connect to no problem. i tried hard resetting the asus router, power cycling both multiple times

after power cycling the gateway router i can connect to the 5ghz for a short time and get the speeds i used to, but afterwards it disconnects. all other devices can conect to the 5ghz network without issue

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what do i do