Don't have many useful suggestions apart from trying to wire in your Decos to a compatible switch or try to wire as many as you can to your main mesh unit directly then use wireless backhaul for the rest. I was getting STP/network loops but never realized the issue was the concurrent wireless backhaul while wired in.

Please TP-Link give us the option to disable wireless backhaul completely when ethernet is connected. It is causing STP across my network and many others and I don't think it makes any sense to have wireless+wired backhaul since it won't exceed a wired 10GbE experience.