Just bought an AXE5400 (3-pack XE75) new, installed around my house, works fine except for three issues...

1.  I have some devices that can operate on 2.4 or 5 GHz but I want them to only use 5.  In the Deco phone app under Connection Preference I have set them to only use 5 GHz and only use the Deco station in my kitchen.  I've also turned off Mesh Technology because these devices don't move.  The phone app shows they are locked to the right band and location, but I come back the next day and they're showing up on 2.4 GHz.  Is this Connection Preference in the Deco app supposed to be a true "lock" but the software/firmware is not working, or just a "preference" and they can shift to the other band under certain circumstances?  I know I can set up a separate 5 GHz SSID but I'm trying to understand if this is broken or working properly and I just don't understand how it's supposed to work.

2.  I have about 40 wifi devices in my home, for most of them I am setting Connection Preference for band and location, custom name/icon, and turning off Mesh Technology for various reasons.  I am not using QoS Priority.  For most devices the custom settings I'm entering do stick, for some of them they don't, they revert back to Mesh, or the wrong band, or the default name broadcast by the device.  I go back and set them again and it sticks for a random amount of time and them reverts.  Is this a known problem?

3.  I have devices dropping off the network and re-joining alot.  It mostly happens when I change settings, so I'm thinking there's some rebooting or internal resetting that's causing this after I change a Preferred Connection, but not sure.  Sometimes things drop and don't come back unless I twiddle with that device, like my front door lock.  If I unlock it by hand it will connect to wifi and let my phone know (device to app) but if I use the door lock app on my phone to reach the door to unlock it, sometimes it can't reach it (app to device) unless I go unlock it by hand again.  Why do devices drop off the router so often and is there something that can be done to stop this?  Some kind of "keep-alive"?

I appreciate any advice or help