Hello @Xema
1. May I know how about the Leds status when RE lose Internet, here is a detailed troubleshooting guide, kindly give it a try and let us if it helps:
https://community.tp-link.com/en/home/forum/topic/272398
2. If power completely goes off on extender, some Model has Power Schedule feature, try to turn it off
How to log into the web management page of the range extender?
1. Visit http://tplinkrepeater.net, and log in with the password you set for the extender.
2. Go to Settings > Advanced Settings > Power Schedule.
May I know the model and hardware version of your range extender? How about the LED status at that time when you notice the issue?