Posting to hopefully help some of the people on this thread, I have AIMesh, with Guest Isolation, Wired backhaul, Main router AX58 and 2 nodes AX55 and AC68, everything works.
The likely issue for at least some people with a similar setup is that if your backhaul goes through a switch, you will have the issue of no IP being assigned unless the switch is managed, supports VLANs and is set up correctly.
The Guest Networks, when isolation is turned on, creates VLANs with IDs of 501 for 2.4GHz (the 192.168.101.XXX sub net) and 502 for the 5GHz (192.168.102.XXX sub net). No VLANs are created or needed when isolation is off.
I have my nodes each going through 2 switches (1 Netgear, one TP-Link) but they are both managed and support 802.1Q-based VLAN's and once those were correctly set up the nodes both worked correctly.