Stable after 2 days of running in an active network with 20-30 clients and:
1. AC86U main 386.9 firmware. Previously 386.7_2
2. 3 Aimesh nodes: AC66UB1 (wired), AC68U (wireless), AX52 repeater (wireless) - all running stock firmware.
Operationally, the network is running smooth - no disconnections etc. So I recommend updating.
But the long-standing problems with Client List and Wireless Log being completely unreliable persist, tho; a number of clients is lacking, especially in the wireless Log, and new clients don't appear even in the Client List until I do a reboot (doesn't cure the Wireless Log tho, only marginally improves is). This makes monitoring the network difficult, and I wish some effort could be put into improving this. I don't know if the official AsusWRT is better than Merlin in this respect.
Another problem I experienced was when I tried "binding" a client (nintendo switch) to an Aimesh node in the iOS Asus Router app (because it suddenly connected to the closest Aimesh node instead of the closest). Now it seems stuck; "unbinding it in the app doesn't unbind it (I click "unbind", dialogie appears asking: "are you sure you want to...", I click "Yes", but it it still "binded in the client list with a RJ45 adapter icon on the right instead of the correct wireless/5ghz icon).