For clarity as I am only on my 1st coffee – does Ethernet Backhaul work if both AiMesh Primary and Node are next to each other connected together by short ethernet cable ?
What is HP Switch model as maybe switch is not picking up (identifying) MAC addresses etc. as switch does need to be a L2 type.
If plugging an Ethernet cable between Aimesh primary and node does work for ethernet backhaul, then try the same setup but connecting both Primary and Node directly to switch to see if the switches routing table is the problem ?
Trial and error I am afraid 
In a completely sane world, madness is the only freedom (J.G.Ballard).
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