Interesting, what is device [44:a8:fc:de:65:6a] ? and was this event log around the time the Aimesh backhaul dropped to 2.4GHz ?
If disabling roaming assistant for you backhaul doesn’t prevent wireless backhaul from dropping to 2.4GHz, I would suggest you factory reset your AiMesh XT8 routers (all) and rebuild all (factory reset all) your mesh system from scratch 
Edit: as per @larryr comments below, could the XT8 router or node be rebooting without your knowledge ?
In a completely sane world, madness is the only freedom (J.G.Ballard).
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