HomeKit Matter Devices randomly unreachable multiple times a day

I have around 30 matter devices as lights, switches and buttons (mostly EVE and Nanoleaf). Additionally I am using multiple HomePod Mini as Thread Border Routers. Unfortunately all the devices are randomly unreachable without any clear reason.

I have attempted a complete reset of all the devices including Factory reset of lights, switches, sensors, Buttons and speakers, a network reset of all iOS devices and a factory reset of the WiFi mesh network.

I ensured multiple times there isn’t other Thread or zigbee networks causing interference and that all the hardware is supported.

that did not help and the issue is still happening. Apple Support with HomeKit could not provide any solutions.

is anyone facing a similar problem? How did you solve it?