I'll try to summarize our stable ZenWiFi BT10 mesh configuration here. I have two IoT networks, one that's 2.4GHz. and for security cameras, electric blanket, internet radio, etc. The other IoT network is 5GHz., and only for the upstairs XT8 in media bridge mode for the HDhomerun connected to our TV's. Then our main network is 5 and 6GHz. only using "smart connect", with wifi-7 turned on, and with MLO wireless backhaul. That's the only place that I'm using MLO, just in the backhaul between the BT10 nodes, and that's very stable and fast. The MLO backhaul is close to as fast as wired backhaul would be, we see very close to our ISP's speed just about everywhere in the house. Not using IPv6 at all. Same firmware version that you're using.
The messages that I saw in your log are mostly standard messages that you should be able to ignore (wlceventd), but there's so many of them that you can't really see the significant ones. I'd suggest trying these commands via ssh:
nvram set log_level=5
nvram commit
reboot
which gets rid of most of the noise-level wlceventd log messages. I usually throw in a couple of "nvram get log_level" commands to make sure that I've done what I came to ssh to do. I also get the "
Mar 26 22:54:31 kernel: WLC_SCB_DEAUTHORIZE error (-30)
Mar 26 22:54:31 kernel: WLC_SCB_DEAUTHENTICATE_FOR_REASON err -30
Mar 26 22:59:35 kernel: SBF: dhd0: INIT [6a:7b:6b:1d:d5:da] ID 65535 BFW 65535 THRSH 2048
sort of messages, which again, have no effect for me. Most of them are for mobile devices, and don't seem to have any effect on the operation of the mesh.
Anyways, we've had great service from the mesh here...your problems may have to do with settings, or may have to do with your mixture of IoT devices, or, of course, your hardware could actually not be working right. Curious if you tired a factory reset for all nodes, and manually setting up your mesh configuration after that? That's helped me several times over the years, worth doing if you're having problems. Also, I really don't feel the need for wired backhaul here, this mesh seems to be designed for wireless backhaul even though it accommodates wired backhaul. But that's just my perception of it. We also had a ZenWiFi AX mesh back in the day, and that too worked great with wireless backhaul...although MLO adds another dimension to wireless backhaul for the BT10's, and really seems to boost it's performance.
Hope this helps. As I've mentioned several times, we get great performance and stability with this mesh, very happy with it. One other stray thought, I've also used the mesh in AP mode with a "wired-only" main router. That also worked really well.