Wi-Fi extender randomly loses connection

Question

I own a TP-Link repeater (TL-WA850RE) which connects via Wi-Fi to my main device (router & AP) and extends the range of my Wi-Fi to rooms that can't be reached by the AP of the main device. The repeater has a constant connection (70-80%) to the main device and works quiet good, if it doesn't decide to stop doing so. The first few months the repeater worked pretty well (not 100%, but a restart of it wasn't required that often. I assumed it sometimes got into an IP conflict and just restarted it. It didn't bother me at this time).

But since a week ot two I can't work anymore because of constantly appearing network problems. My notebook or smartphone are showing a connection but no internet access ("Connected, no internet"). So I changed the default settings of the TP-Link repeater.

My router (main device) has DHCP activated and it was already deactivated on the repeater. I changed the IP of the repeater to a static one and ensured, that it isn't in the range of the DHCP IPs.

• Main Device/Router: 192.168.178.1
• Repeater: 192.168.178.2
• DHCP-Range: 192.168.178.20 - 192.168.178.200
• All Subnet masks are 255.255.255.0

But even now the problem appears so I guess it wasn't an IP conflict at all.

Both, the main AP and the repeater have the same SSID, changing it to two different SSIDS didn't help either. When the connection is lost ("Connected, no internet") I can neither connect to the repeater nor to the main device/router via the repeater. But if the device connected via the main device it still has access to the internet. The cable connected device are not affected by this problem.