Not getting a DHCP IP?  Instead getting:

169.254

169.254.149.164

The tcpdump of the traffic from the affected DD-WRT router shows the DHCP sending over a valid IP yet said IP address is not assigned to the 5Ghz WIFI band?

23:54:16.735841 bb:bb:bb:bb:bb:bb > aa:aa:aa:aa:aa:aa, ethertype 802.1Q (0x8100), length 366: vlan 1, p 0, ethertype IPv4 (0x0800), (tos 0xc0, ttl 64, id 27979, offset 0, flags [none], proto UDP (17), length 348)
    192.168.0.6.67 > 192.168.0.144.68: [udp sum ok] BOOTP/DHCP, Reply, length 320, xid 0xaf0ee6f3, secs 25, Flags [none] (0x0000)
          Your-IP 192.168.0.144
          Server-IP 192.168.0.6
          Client-Ethernet-Address aa:aa:aa:aa:aa:aa
          Vendor-rfc1048 Extensions
            Magic Cookie 0x63825363
            DHCP-Message (53), length 1: Offer
            Server-ID (54), length 4: 192.168.0.6
            Lease-Time (51), length 4: 86400
            RN (58), length 4: 43200
            RB (59), length 4: 75600
            Subnet-Mask (1), length 4: 255.255.255.0
            BR (28), length 4: 192.168.0.255
            Domain-Name (15), length 7: "dom.abc"
            Unknown (252), length 1: 10
            Domain-Name-Server (6), length 20: 192.168.0.30,192.168.0.10,192.168.0.20,123.87.80.1,123.87.81.1
            Default-Gateway (3), length 4: 192.168.0.6
23:54:17.580935 cc:cc:cc:cc:cc:cc > ff:ff:ff:ff:ff:ff, ethertype 802.1Q (0x8100), length 594: vlan 1, p 0, ethertype IPv4 (0x0800), (tos 0x0, ttl 64, id 0, offset 0, flags [none], proto UDP (17), length 576)
    0.0.0.0.68 > 255.255.255.255.67: [udp sum ok] BOOTP/DHCP, Request from cc:cc:cc:cc:cc:cc, length 548, xid 0x9035706b, Flags [none] (0x0000)
          Client-IP 192.168.0.210
          Client-Ethernet-Address cc:cc:cc:cc:cc:cc
          Vendor-rfc1048 Extensions
            Magic Cookie 0x63825363
            DHCP-Message (53), length 1: Request
            Parameter-Request (55), length 5:
              Subnet-Mask (1), Default-Gateway (3), Domain-Name-Server (6), Domain-Name (15)
              Hostname (12)
            Hostname (12), length 10: "RokuPlayer"
23:54:25.476020 bb:bb:bb:bb:bb:bb > aa:aa:aa:aa:aa:aa, ethertype 802.1Q (0x8100), length 366: vlan 1, p 0, ethertype IPv4 (0x0800), (tos 0xc0, ttl 64, id 28795, offset 0, flags [none], proto UDP (17), length 348)
    192.168.0.6.67 > 192.168.0.144.68: [udp sum ok] BOOTP/DHCP, Reply, length 320, xid 0xaf0ee6f3, secs 34, Flags [none] (0x0000)
          Your-IP 192.168.0.144
          Server-IP 192.168.0.6
          Client-Ethernet-Address aa:aa:aa:aa:aa:aa
          Vendor-rfc1048 Extensions
            Magic Cookie 0x63825363
            DHCP-Message (53), length 1: Offer
            Server-ID (54), length 4: 192.168.0.6
            Lease-Time (51), length 4: 86400
            RN (58), length 4: 43200
            RB (59), length 4: 75600
            Subnet-Mask (1), length 4: 255.255.255.0
            BR (28), length 4: 192.168.0.255
            Domain-Name (15), length 7: "dom.abc"
            Unknown (252), length 1: 10
            Domain-Name-Server (6), length 20: 192.168.0.30,192.168.0.10,192.168.0.20,123.87.80.1,123.87.81.1
            Default-Gateway (3), length 4: 192.168.0.6
 

Particularly on the 5Ghz signal.  In this case, leaving TurboQAM and NitroQAM enable however disabling Implicit Beamforming and Explicit Beamforming fixed the problem.  Apparently a self inflicted wound.  Had this disabled earlier and just recently reenabled.

Some handy commands:

tcpdump '(port 67 or port 68) and ether host aa:bb:cc:dd:ee:ff' -e -n -vv

HTH