The Deco network optimization does not, and cannot, always do a good job of selecting the channel. In some situations a manual override would give a better result. 

This is one of the reasons I gave up on Google nest router - it would always pick the same channel as my neighbor.

My Deco does the same thing, picks the same channel as my neighbor - on 2.4 and 5 Ghz. My neighbor's router is next to my TV while my router is quite a bit away, so perhaps they seems like a choice from where my router is, leading to that I cannot use my TV over wifi. 

So: please add the option of manually setting the channel.