@Cepheus0815 

When you reserve the IP address it uses the MAC Address to see if that device has a reserved IP, if so DHCP will assign that IP. If your devices are getting a different IP than expected, you may have one or more of the following issues:

1. You have more than one DHCP server
2. The device in question may be randomizing the MAC address each time it connects. Cell Phones do that by default.
3. Wired and Wireless network adapters will each have their own unique MAC address, so if you reserved the IP using the Wired MAC address, Wireless would not get the reserved IP.

  @HellBent thanks for the quick response. Actually the MAC did not change. One of the devices is even a TP link switch. I am pretty confident, I have only one DHCP server, which is my Omada gateway. When I turn the power off from all my network devices and restart again, it is most of the time back to normal. No idea, where these wrong assignments are coming from. Any chance I can debug that? 

Thanks, Rainer

  @Cepheus0815 

I only use the Software Omada Gateway for my WiFi AP's. I have not connected my router yet because I would lose the switch ports that I'm using for different LANs vs VLANs, so I do not have experience with the Omada Gateway DHCP.

You should check to see if the is an Omada Software update or a Firmware update if you are using the hardware gateway.

Next time you run into this issue, before rebooting your devices, try renewing the IP from the device first to see if it gets the correct IP. I have also seen that some DHCP servers will have reservation limits and if you have too many reserved IPs, some won’t work.