@ytakagi i faced the same problem and the suggested solution of removing all "spaces" from description works.

THIS IS REALLY STUPID!! who the f**k writes codes that breaks when the text strings of inputs contains "spaces"!! how f**king stupid is this!! wasted 3 hours of my time restarting and rebooting and researching.

f**king stupid chinese products.

Dear All,

I have had the same DHCP assigning issue with the new firmware ver. < c9v5_eu-up-ver1-2-4-P1_20190403-rel63869 >. It happens only if the WAN port is adjusted at static IP address. To avoid this problem, I have found a solution down below:

• Follow the steps to set up the router for first time with a cable. Do not make any address reservations or any other changes. Just set a password. Do not connect any clients to the router accept the PC you use for adjustment.
• Do not allow a firmware update from the air. You need to download the latest firmware version from the official European site in your PC first. Then use “Manual Update” of the firmware.
• After restarting you need to have an internet connection at your PC. If it is o.k, connect all your clients to the router. Wired or wireless, as you wish. WERY IMPORTANT! Be sure, all the clients have an internet connection and working well.
• Now it is the right time to open the Address Reservation submenu and to start to enter the MAC addresses and their corresponding IPs. You are free to assign any IPs to any corresponding MAC address. After that you need to disconnect everyone client with reserved IP address and switch it off (very important!). After minimum 10 seconds you can connect it again after restart. Do this sequentially for everyone client. Pay attention with devices running Android 10! They MUST NOT USE randomized MAC address function which is set by default! You need to change it on “device MAC address”.

Good luck!

@edison_zhang 

The same problem is for the Archer D9. There is no description field in the reservation address but I am having the same problem. Driving me mad :(

Also, the latest firmware is "Published Date: 2015-08-26" which I doubt fixed this problem being this thread dated 2019. What should I do? BTW I use the D9 as a c9, I. E only router function