Hi,
Try the following, you will need access to the command line (Accessing the command line - General - OSMC)
sudo rm -rf /var/lib/connman/wifi*
Then via my myosmc try connecting to the 5g network again, you will need to re-enter your password.
Now please debugging logs, try playing a movie via NFS; reboot and upload logs. Details on how to do this can be found here:
Thanks Tom.