I can confirm that with 41535 on my AX88u and two ac68u aimesh nodes if I enable a guest network which has no intranet access and sync to all nodes then devices on those nodes will drop many packets. Changing to not sync to aimesh nodes fixed it. (Reboot of nodes needed this time). Ethernet backhaul is enabled.
I also get this using an AX88U and AC67U nodes. I am pretty sure AC67U uses the same firmware as AC68U. I am using the official released 386 firmware, not any of the RCs. Asus please fix this!
P.S. I have a ticket logged with Asus support for this.