When you say it is UP to date, can you post the versions of firmware and software please ?
I'm assuming you already tried to toggle the WiFi on/off ? If the box is configured to always "suspend" rather than power off ,can you please try by unplugging power to the box, wanting 5 seconds and the plugging it back in. Suspend mode can have some strange side effects which accumulate over time.
Most importantly. Has this been an issue from the beginning or did it just start occurring ? How long have you owned the box, is it possibility still under warranty (check checking) ?
If all else fails, you can try doing a hard factory reset and see if that fixes it. You can backup your server settings/favorites to a USB stick first (to make at least BuzzTV 5 easy to reconfigure afterwards). But any 3rd party apps would need to be reinstalled. If it is a software glitch, this can help. However if it is an underlying hardware failure of the 5Ghz radio, then there is not much that can be done. BTW: Did you try swapping the antenna (between left and right or even with other box) ? Maybe one of them is just dead.
Different box, but exact same procedure :
https://stbtalk.com/topic/300-factory-reset-hard-reset-xr4500-xrs4500/