I have the following network layout: ISP modem -> AX80 EU version -> RE705X running latest firmware. Both AX80 and RE support EasyMesh.

AX80 is in livingroom and RE is in a balcony, with ethernet cable available.

Until today, RE was functioning ok, connected via cable to that ethernet port (which leads to a TL-SG108E) reporting that is wired linked (975Mbps <- not sure why not 1000Mbps), with devices connected to it reaching close to my ISP connection (1000/25)

Today RE started acting strange, losing internet, and after 3-4 hours of restarts and resets, I have it up & running sort of ok. Sort of ok because although is reporting that is linked wired, same 975 Mbps, the speeds when connected to it barely reach 200 Mbps. There are moments when I can see spikes to ~500 Mbps and something happens like a brief loss of internet connection. Speeds via wireless of router are ok, reaching 1000/25. 

Since the connection led is red, signaling that RE is too far from router, but router reports a wired connection with RE, since until today it was functioning as linked via wire, with speeds close to 1Gbps, what could cause the current issue of low speeds? 

What's the ethernet backhaul support for this model? Is it functional as of firmware 1.1.4?

OneMesh should be disabled in both devices, in Tether app, considering that EM is active?