Some of my devices (especially on the 2.4 band) don't play nice with certain channels. Running the network optimisation helps - but then I'll often find that at some point the Deco changes the band and so I lose connection to some devices. Only way to restore is to run optimisation again. 
 

I get that the Deco tries to decide channels itself intelligently but there needs to be an option to override this and manually select channels. 
 

Similar issue on 5ghz band - where some devices (eg Ring) don't work on certain channels - but is no way to force the selection.