Could you share a troubleshoot file for the device in which you have configured 5Ghz client and its unable to provide internet access to the LAN devices . (The event must be logged in the troubleshoot file).
Configure the 5ghz client and try to keep device on for 10-15 minutes before downloading the troubleshooting file.
Troubleshoot file could be downloaded in System>Administration>Troubleshoot.
I have tested it on my side and its not working on my side as well. After configuring 5Ghz client also check if device has internet from 5Ghz wireless WAN interface. You can check it in System>Administration>Troubleshoot>Diagnostics.
Share troubleshoot file in DM and for DM you need to signup .