Hmm - prompted by your post I did a little testing. I have 3 x AP906 in a mesh system. If I set the bandwidth on their 2.4GHz band to "Auto 20/40" then all devices connected on 2.4GHz show as connected with 20M bandwidth. If I set the bandwidth to 40 then some devices decide to connect at 40M and the others still connect at 20M. So what is the purpose of the "Auto 20/40" setting one might ask, and if some devices still connect at 20M when the setting is 40M why bother having a bandwidth setting at all? Just leave it at the highest value and let the devices decide...I see the same behaviour on my 2927ax router on the 2.4GHz band.