@Ysp 

As mentioned, I had changed it from its default settings (auto) to 80 Mhz, after I changed that back it resolved it issues (at least for me, I haven't put it back to 80Mhz to see if the issues would return). 

Anyhow, you can see and change that setting if is select your device for the device list, select "config" and look for "Radios" as shown below in the screenshot. (this setting can be set on per AP basis)

  @Ysp 

Sadly TP-LINK is aware of this issue and I was told there would be a fix shortly. I asked them to simply PULL the bad firmware off their update list for now. But I still continue to see my OC300 recommending it. 

I have decided, my network is good for now so I just disregard the update noticed. Though the Firmware in the ER707-M2 VPN router still has some issues.   

In my network I have ER8411, OC200, 33 eap's which are still increasing. Most are EAP225 Outdoor hardware version 1 and 3, and 14 EAP225 are connected wirelessly. Everything worked reliably for months until suddenly 6 started disconnecting. I have the radio set to automatic. I didn't see this thread because I didn't have any problems. On all EAP225-Outdoor(EU) I have firmware 5.1.6. In the coming days I will downgrade to 5.1.1 and move to software controller. As I went past the 33 EAP limit the OC200 controller started disconnecting and rebooting, I assume it is faulty.

theres a new beta firmware for the er707-m2, but i don't think it fixed the problem, even with alos a beta for the 225 outdoor (5.1.7) i think it has problemes, went back to 5.1.1 and everything ist okay again.