If you re-enable the 5GHz network what happens?
I am not sure how the Hub4 works - never seen one - so someone else needs to comment - but the standard advice for the Hub3 is to switch off channel optimisation/smart wifi and rename the SSID's of the two bands to separate them out. Dunno if you can do that on the Hub4.
Alternatively - put it into modem mode and use your own better quality equipment
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John
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I do not work for VM. My services: HD TV on VIP (+ Sky Sports & Movies & BT sport), x3 V6 boxes (1 wired 2 WiFi,) SH2 in modem mode with Airport Extreme Router +2 Airport Express's. On VIVID200, Talk Anytime Phone, x2 Mobile SIM only iPhones.