I have a couple access points set for 5 MHz bandwidth using 5 GHz frequencies. I just purchased several Groove 52HPn radios, and they will not see the access points, even when the AP and client (Groove running Level 3) are set to 5 MHz. If I put both back to 20 MHz, things seem to be fine. Does anyone know what is going on here?

please make sure that you are using the latest RouterOS version.

I had similar issues. I think my 52Hn's came with 5.24, upgraded to 5.25 and half and quarter channels now work.