Did you ever find a solution for this?  Getting the same issue on the same hardware revision and firmware.  I did notice that all DHCP allocated addresses switch to "Perminent" wether I've set a static IP for that device or not.  Also, it did not work to just disable entries.  I had to remove them before my DHCP server started allocating addresses again.  I might try a factory reset or firmware downgrade and update here for anyone else facing the issue.

I had this exact issue, DHCP would completely stop when assigning a reservation, and deleting reservations would enable DHCP again. I found an article on the forum where someone was having this problem with a different model of TP-Link router that they were able to fix this by deleting any spaces or special characters in the hostname. I have the Archer C9 v5.0. I was using a space in the "Description" field.  So I attempted using no spaces and it solved my issue. This may very well be other peoples issue.

TL:DR-  Try deleting any spaces or special characters (#,-,!, ect.) in the "Description" box of the reservation.

I created an account to report this issue, but it seems that you may have already solved this.  I had unintentionally verified this with one entry which used underscore's instead of spaces, and the second entry had a space in the description.  The moment I removed the one entry with spaces in the description, DHCP started working for all other devices on my network.  Once we're done with our meeting, I'll test adding a second entry without using spaces.

Thank you!

c5-R wrote

I had this exact issue, DHCP would completely stop when assigning a reservation, and deleting reservations would enable DHCP again. I found an article on the forum where someone was having this problem with a different model of TP-Link router that they were able to fix this by deleting any spaces or special characters in the hostname. I have the Archer C9 v5.0. I was using a space in the "Description" field.  So I attempted using no spaces and it solved my issue. This may very well be other peoples issue.

 

 

TL:DR-  Try deleting any spaces or special characters (#,-,!, ect.) in the "Description" box of the reservation.

c5-R wrote

I had this exact issue, DHCP would completely stop when assigning a reservation, and deleting reservations would enable DHCP again. I found an article on the forum where someone was having this problem with a different model of TP-Link router that they were able to fix this by deleting any spaces or special characters in the hostname. I have the Archer C9 v5.0. I was using a space in the "Description" field.  So I attempted using no spaces and it solved my issue. This may very well be other peoples issue.

 

 

TL:DR-  Try deleting any spaces or special characters (#,-,!, ect.) in the "Description" box of the reservation.

This worked for me as well.  Thanks so much for posting! I'll report back if any issues occur after.

Current firmware: 1.2.2 Build 20180423 rel.85787(5553)

Hi All,

I have (had) a Ver.5.1 device running <c9v5_eu-up-ver1-2-4-P1_20190403-rel63869> firmware. The ISP offers me a static IP. After the adjustment the router cannot assign IPs to its` clients. Only cable connected clients with reserved IPs can use internet. When I adjust the router like an extention of my old TL-WDR4300 using a dynamic IP on my WAN port, DHCP works fine and all the devices obtain IPs. So I sent back the new Archer C9. Please inform me what router can I use for my home network? I just need an USB printer controller and USB 3.0 port for FTP server. Thank You.