The camera is exhibiting unexpected behavior. The expected behavior is to be able to connect at 5GHz with just the one setting change. Are you sure your router or mobile phone is set to 5GHz only or 5GHz preferred?
I’m not sure what the source of the problem is. You can try
reset wifi
RICOH THETA Z1 Wi-Fi Reset - #5 by craig
- press WiFi and mode for 11 seconds
- camera will reboot
- after reboot, set to 5GHz again and try it with your mobile phone in AP mode as a test
reset all settings
Same as above, except use this API to reset all settings
other options
- call official RICOH customer support Contact | RICOH THETA
- if outside of US RICOH IMAGING
- The Z1 runs Android inside of it. Search for Android cannot connect at 5GHz on Google Search and try to isolate the problem.