Hello, I have never seen this error but it seems weird to me that it says "sending packet to 18.104.22.168 on interface 169.254.1.1/br14/33" and is because the IPs. The controller is receiven and IP through DHCP or it use a static address?
Have you check the CPU and number of connections that is having the AP?
Are they running IPv6 by any chance? We have a bug AP-3347: Solo AP 22.214.171.124.1347 - IPV6 nDNS, AP not discovered on same IPV6 subnet when I searched on "registration:594". My searches on "nf_conntrack table full, dropping packet" did not hit on any Solo AP issues, only old ZD 9.8 or gaming application drops on 9.5 w/local DHCP. If they are using IPv6, would you please open a trouble ticket with our Tech Support: https://support.ruckuswireless.com/contact-us