My RE450 extender, which I updated to the latest firmware version RE450(EU)_V4_1.0.20 Build 230213 has very unstable speed with high fluctuation. Most of the time I get around 240mbps more or less, but it frequently fluctuates in a variation range of 100mbps or maybe more. The same applies to upload sometimes. When I turn the wifi off and back on in windows, it gives me decent speeds again for some time (between 230 and 240 down and between 150 and 170 up). I have it placed in between the router and my laptop, at more or less 2.5 meters away from each and set on maximum coverage mode. I also have both the door of the way to the router and the door of the room where the laptop is closed. I don't know what can be done and/ or if maybe a new firmware version could fix it.

Edit: the tplinkrepeater.net also started to keep not being able to recognize that I am connected to it and doesn't enter the configuration interface, and in the main router config interface the repeater shows up as disconnected. I've reset the repeater to factiry settings several times.