Constantly losing connection to Ikea Switches and Ledvance Smat+ Plugs

Describe the bug

Setup:

Conbee-USB-Stick connected to Raspi-Pi Version: 2.11.05 / 9.5.2021 Firmware: 26660700
Raspi-Pi running FHEM
4x Wall Plugs: LEDVANCE Smart+ Plug (don't know which Firmware)
5x Ikea TRADFRI on/off switch (the rectangular ones)
Several Philips Hue devices & Hue Bridge in house

Deconz was set up roughly 6 months ago. The plugs and switches were paired successfully on initial setup. For that the devices were held close to the USB-stick to get best connection.
After set up the devices were connected and worked
Afterwards sporadically devices lose connection
Unplugging and re-plugging the power outlets did not lead to them being found by Deconz again.
Occasionally devices are found again and work
If a device reconnects it might lose connection a few hours/days/weeks later again
Some devices that lose connection are 4-5m away from the ConBee II stick. No big obstacles in the way (couch or wooden guard rail of a stair case or so).
Other devices that are a floor beneath ans many more meters away of the ConBee II, it rarely loses connection 🤷‍♂️
Setting up additional TRADFRI switches between ConBee II and devices regularly losing connection to enlarge the network, by additional hops, did not help.

No required I guess?

Host system: Raspberry Pi
Running method: deCONZ Add-on
Firmware version: 26660700
deCONZ version: 2.11.05 / 9.5.2021
Device: ConBee II
Do you use an USB extension cable: no
Is there any other USB or serial devices connected to the host system? yes: 1x JeeLink, 1xCul433
Tested the beta: no difference

I didn't have a look at logging yet. Will it give additional information here?

I love the idea behind ConBee / Deconz! However it's super flaky and not really useful for reliable daily usage at home :(