Homekit - some Hubs and bridges are not displaying my HomeKit devices

Hello,

I am currently using the Apple Homekit with around 15+ smart accessories (Lights, security camera, heating, door locks, power outlets). With those I have 4 devices capable of acting as the HomeKit hub - 2x HomePod mini, 2x Apple TV 4K. Everything seems to work perfectly well (all my devices show up in the app and they respond) as long as I don't turn on the "automatically choose HomeKit hub and bridges" function on in the settings of the app. If I manually set any other device as the hub apart from the HomePod that I have in my bedroom, most of the smart devices disappear from the Home app. Depending on which device I set up as the bridge, some of the smart devices inside the app do and some of them don't show up.

I believe it's not because of connection issues with my router since I have set up a Wifi base in my home by using one Apple Airport Timecapsule + two Airports extremes. The signal on my iPhone is showing up as very strong in every corner of my house. This thinking is also supported by the fact that my Security camera (which is located outside, at the weakest signal point) is the only accessory that is always working no matter what device is acting as the hub.

I tried all of the basic advices, like resetting each of the hubs and reconnecting them, setting all of my devices to the newest system (yes, also all of the iPhones and Macs of everyone in the family). Same with turning off and resetting the Airport stations. The only thing I didn't do is delete the whole Home and create a new one and connect and setup everything from scratch. I am really hopeful that someone helps me to find a solution instead of that because that would take at least a few hours.

Thank you for your help!!