DIAGNOSIS Your phone or device likely lost the connection because the router's 6 GHz band (Wi-Fi 6E) is either disabled or its settings were changed. The 6 GHz band has stricter regulatory controls and can be configured to turn off under certain conditions in the router's settings.
FIX Log into the router's admin page. Go to Advanced > Wireless > Wireless Settings. Look for the 6 GHz band section. Ensure the 'Enable Wireless Broadcasting' checkbox is ticked. Also, check the 'Control Channel'. If it's set to 'Auto', try manually selecting a channel like 37 or 93. The 'Enable SSID Broadcasting' box must also be checked for it to be visible.
IF THAT DIDN'T WORK The 6 GHz band uses something called Automated Frequency Coordination (AFC). If the router thinks it's in a location (based on the country/region code you set during setup) where 6 GHz operation isn't allowed or needs special coordination, it may disable the band. Go to Advanced > System Tools > System Parameters and verify the Region is set correctly.
HEADS UP Not all devices support all 6 GHz channels. Some older Wi-Fi 6E clients only support the lower part of the band. If you manually set a control channel above 149, some phones might not see it. Sticking to channels 37-117 is generally safest for broad compatibility.